Polymer-coated carbon-clad inorganic oxide particles

ABSTRACT

Polymer-coated carbon-clad inorganic oxide particles are disclosed which are useful in sorbent applications, particularly as packing materials for High Performance Liquid Chromatography (HPLC). A method for the preparation of a chromatographic support material is also disclosed which comprises coating carbon-clad inorganic oxide particles with a monomer or oligomer and cross-linking the monomer or oligomer.

This is a continuation of application Ser. No. 07/497,595, filed Mar.22, 1990, now abandoned.

FIELD OF THE INVENTION

The present invention provides polymer-coated carbon-clad inorganicoxide particles which are useful as a chromatographic support material.The invention also provides a method for forming a chromatographicsupport material, by coating carbon-clad inorganic particles with amonomer or oligomer, and cross-linking the monomer or oligomer to formpolymer-coated carbon-clad particles.

BACKGROUND OF THE INVENTION A. Inorganic Oxide-Based ChromatographicSupports

Currently known inorganic chromatography supports , comprisingparticulate silica (SiO₂) or alumina (Al₂ O₃) are stable over pH rangesof about 1-8 and 3-12, respectively. The solubilization of SiO₂ and Al₂O₃ at pHs outside of these ranges results in the deterioration of thesesupports, and in contamination of the resultant chromatographed andseparated products with silicon- or aluminum-containing species. Methodsof improving the alkaline stability of particulate SiO₂ by cladding thesurface with a more base-stable metal oxide such as zirconium oxide(ZrO₂) have been disclosed in U.S. Pat. Nos. 4,648,975 and 4,600,646.This cladding is disclosed to increase the upper pH limit at which thesesupports, also referred to as packings, can be used to 11 and 9.5,respectively. However, these packings still lack adequate stability toallow them to be sterilized and cleaned in, for example, 0.1N aqueoussodium hydroxide (NaOH, pH=13).

Use of porous spherical ZrO₂ particles on a thin layer chromatographyplate is disclosed in U.S. Pat. No. 4,138,336; a process for thepreparation of porous ZrO₂ microspheres is taught in U.S. Pat. No.4,010,242; and chromatographic use of these particles is taught in U.S.Pat. No. 3,782,075. The microspheres are prepared by a process in whichcolloidal metal oxide particles are mixed with a polymerizable organicmaterial and coacervated into spherical particles by initiatingpolymerization of the organic material. This is a time consuming, batchprocess which requires the addition of organic material which is laterpyrolized and hence lost.

U.S. Pat. No. 3,862,908 discloses microspheres of urania and other metaloxides; however, these particles are fired to near full density, havereduced surface areas and therefore, would not be desirable forchromatographic uses.

U.S. Pat. No. 3,892,580 discloses a process for preparing porous bodiesof ZrO₂. This process requires the use of a binder to react with theoxide particles during preparation. This binder is subsequentlydecomposed by pyrolysis and therefore lost. The bodies produced by thisprocess are not spherical, would pack unevenly, may cause increasedcolumn pressure, and are therefore not preferred for chromatographicuses.

U.S. Pat. No. 4,389,385 teaches the preparation of porous gels andceramic materials by dispersing solid particles of an inorganicsubstance produced by a vapor phase condensation method in a liquid toform a sol. The sol contains colloidal particles which are aggregates ofthe primary particles. The sol is dried to produce a porous gel ofgreater than 70% by volume porosity.

Commonly-assigned U.S. patent application Ser. No. 07/420,150, filedOct. 11, 1989, now U.S. Pat. No. 5,015,373 discloses a support materialadapted for use as the stationary phase in liquid chromatography (LC),which comprises ZrO₂ spherules preferably having a diameter of about0.5-200μ, a surface area of about 1-200 m² /g, and pore diameters ofabout 20-500 Å preferred embodiment of the invention disclosed in the'150 application is directed to a chromatographic support materialcomprising ZrO₂ spherules having a cross-linked polymeric coatingthereon, wherein the coated spherules are hydrophobic, have a pore sizefrom about 20-500 Å and an average diameter of about 0.5-500μ.

B. Carbon-Based Chromatographic Support Materials

Carbon particles, such as those referred to as "activated carbon," areemployed in sorbent applications due to their relatively high specificsorption capacity. This capacity is at least partially due to carbon'slow density and the fact that it can be made highly porous.

Carbon has also been employed in chromatographic applications because itoffers a hydrophobic and hydrophilic, selectivity which is differentthan that of the silica supports commonly utilized in reversed-phaseHPLC. See, e.g., K. Unger, Analytical Chemistry, 55, 361-375 (1983) atpage 372, column 3. Carbon's selectivity to polar compounds also variesfrom the selectivities of conventional HPLC packing materials. Thesedifferences in selectivity can be advantageously exploited.

A further advantage of carbon-based supports is their pH stability. Thisstability allows separations to be performed at the optimal pH, and alsopermits cleaning and sterilizing of the column with, for example, strongbase.

Packing materials for high pressure liquid chromatography (HPLC) havealso been based on carbon. For example, carbon-based supports useful forHPLC applications have included the following: graphitized carbon black(GCB), pyrocarbon reinforced GCB, and more recently, a porous graphiticcarbon (PGC). PGC is prepared by filling the pores of a silica gel witha polymer comprising carbon, thermolyzing the polymer to produce asilica/carbon composite, dissolving out the silica to produce a porouscarbon, and subjecting the porous carbon to graphitizing conditions.

For example, U.K. Patent Application No. 2,035,282 discloses a methodfor producing a porous carbon material suitable for chromatography oruse as a catalyst support, which involves depositing carbon in the poresof a porous inorganic template material such as silica gel, porousglass, alumina or other porous refractory oxides having a surface areaof at least 1 m² /g, and thereafter removing the template material. O.Chiantore et al., Analytical Chemistry, 60, 638-642 (1988), disclosecarbon sorbents which were prepared by pyrolysis of either phenolformaldehyde resin or saccharose on spheroidal silica gels coated withthese materials. The pyrolysis is performed at 600° C. for one hour inan inert atmosphere, and the silica is subsequently removed by boilingthe material in an excess of a 10% NaOH solution for 30 minutes.Chiantore et al. conclude that, at the temperatures employed in theirwork, the carbonaceous polymer network that was formed still maintainedsome of the chemical features of the starting material (page 641, column2). To obtain carbons where polar functional groups have been completelyeliminated, the authors conclude that high temperatures (greater than800° C.) treatments under inert atmosphere are necessary.

The use of pyrocarbon-reinforced carbon-based supports for HPLC is alsoknown. For example, K. Unger et al. (U.S. Pat. No. 4,225,463) discloseporous carbon support materials based on activated carbons and/or cokes,which may be useful for HPLC. The materials are prepared by treatinghard activated carbon or coke particles with solvents, and then heatingthem at 2400°-3000° C. under an inert gas atmosphere. The resultingsupport materials are disclosed as having a carbon content of at least99 percent, a specific surface area of about 1-5 m² per gram, and aparticle size of about 5-50 μm (column 2, lines 3-5).

While carbon or carbon-based materials may be useful as HPLC supports,they are less than ideal. For example, K. Unger, Analytical Chemistry,55, 361-375 (1983) concludes that the carbon materials developed forHPLC to date exhibit poor efficiency for strongly retaining compounds.

C. Non-Carbon Based Materials having Carbon Coatings

In addition to materials which comprise a carbon matrix or core,chromatographic support materials are known which have a carbon coatingon a substrate of silica. For example, N. K. Bebris et al.,Chromatographia, 11, 206-211 (1978) disclose the one-hour pyrolysis ofbenzene at 850° C., onto a substrate of Silochrom C-120, a macroporoussilica (SiO₂) which contains particles of irregular form with an averagesize of 80 μm. Benzene pyrolysis was also carried out at 750° C. onto asubstrate of Spherisorb S20W, a silica gel which contains sphericalparticles of diameter 20 μm.

R. Leboda, Chromatographia, 14, 524-528 (1981) disclose the two-hourpyrolysis of dichloromethane (CH₂ Cl₂) on partially dehydroxylatedsilica gel (particle size range 0.15-0.30 mm) at 500° C. and atmosphericpressure. R. Leboda et al., Chromatographia, 12, No. 4, 207-211 (1979)disclose the catalytic decomposition of alcohol onto the surface of SiO₂in an autoclave, at a pressure of 25 atmospheres and a temperature of350° C. for 6 hours. The resulting material possesses a surface havingfrom "a few to several dozen percent carbon on the surface." R. Leboda,Chromatographia, 13, No. 9, 549-554 (1980) discloses contacting SiO₂with alcohols (benzyl alcohol and heptanol) in an autoclave at atemperature of 500° C. R. Leboda, Chromatographia, 13, No. 11, 703-708(1980) discloses the heat treatment in hydrogen at 700° C. of SiO₂adsorbents previously treated with alcohols in an autoclave at 500° C.

P. Carrott et al., Colloids and Surfaces, 12, 9-15 (1986) crackedfurfuraldehyde vapor on precipitated silica at a temperature of 500° C.for various times, to achieve carbon loadings of 0.5, 8.6 and 16percent. Carrott et al. conclude that the external surface of theresulting carbon-coated silica was hydrophobic, while the internalsurface was hydrophilic, indicating that the internal surfaces were notwell coated.

H. Colin et al., J. Chromatography, 149, 169-197 (1978) comparesnon-polar chemically-bonded phases (CBP), pyrocarbon-modified silica gel(PMS) and pyrocarbon-modified carbon black (PMCB) as packings forreversed phase HPLC. H. Colin et al., J. Chromatography, 158, 183-205(1978) compares the efficiency, retention and solvent strength inreversed-phase HPLC of the column packings shown in Table III (page190), which include 15-20 um particles of pyrocarbon coated on silica,and 25-31.5 um particles of pyrocarbon coated on graphite. H. Colin, J.Chromatography, 167, 41-65 (1978) reports the effects of temperature inreversed-phase HPLC on pyrocarbon-containing adsorbents, in terms ofheat transfer, solvent eluotropic strength, column linear capacities,pressure drops and efficiencies.

U.K. Patent Application No. 2,035,282, discussed above, also disclosesthat silica gels whose internal surfaces have been covered by a layer ofpyrolytic carbon exhibit good chromatographic performance, but aredisadvantageous in that the presence of a silica core means that eluentsaggressive to silica cannot be used with these gels. Furthermore, it isdifficult to attain complete coverage of the silica surface by carbonbecause the carbon tends to deposit on surface nuclei already present,rather than on the bare silica (page 1, lines 21-26).

K. Unger et al. (U.S. Pat. No. 4,225,463), discussed above, alsodisclose that attempts to mask the surfaces of silica gels withnon-polar groups via pyrocarbon coating have not alleviated theproblematic low stability of SiO₂ to aqueous solvent systems,particularly those with higher pH values (column 1, lines 5-48).

Catalyst supports have also been prepared by deposition of carbon onalumina. For example, S. Butterworth et al., Applied Catalysis, 16,375-388 (1985) disclose a γ-Al₂ O₃ catalyst support having a coating ofcarbon deposited by vapor-phase pyrolysis of propylene. The pure phaseγ-Al₂ O₃ substrate was ground to 12×37 mesh, had a bimodal pore sizedistribution based around mean diameters of 110 nm, and a surface areaof 130 m² /g. When the vapor phase pyrolysis was performed from aflowing gas mixture of argon and propylene at 673K, Butterworth et al.disclose that the pure phase γ-Al₂ O₃ was completely covered at a carbonloading of 7 wt-%.

Certain metal oxides have been coated with carbon for use as nuclearreactor fuels. For example, P. Haas, Chemical Engineering Progress,44-52 (April 1989) discloses that small spheres of oxides of U, Th andPu were required for high-temperature, gas-cooled nuclear reactor fuels.These fuels were coated with pyrolytic carbon or other ceramics to serveas "pressure vessels" which would contain fission products (page 44,column 2). FIG. 2, at page 49, shows dense ThO₂ spheres with pyrolyticcarbon coatings.

D. Silica-Based Stationary Phases for Reversed-Phase HPLC

The majority of separations employing high performance liquidchromatography are performed in the reversed-phase mode, wherein thecolumn packing material serves as the stationary phase. The most commonpresently used stationary phases employ a non-polar ligand (e.g., octaneor octadecane) covalently bound to a porous silica particle through asiloxane bond (Si--O--Si) to render the silica surface hydrophobic.Although these silica-based supports are very useful for a wide range ofapplications in reversed-phase HPLC, their use is strictly limited to apH range of between 2 and 8, due to the hydrolytic instability of boththe silica support particle and the siloxane bond used to "anchor" thenon-polar active group. Thus, a pH-stable, reversed-phase supportmaterial must involve both a stable, controlled-porosity, high-surfacearea support material and a method for rendering the surface durablyhydrophobic.

Art workers have previously coated silica with ZrO₂ in attempts toimprove the silica's pH stability. Another approach to developing ahighly stable reversed-phase support involves replacing the silica withan alternative inorganic material, such as alumina. Although it has beendemonstrated that some improvement in pH stability is realized byreplacing silica with alumina, the dissolution of alumina in aqueoussolutions at extreme pHs (pH<2 and pH>12), at temperatures as low asroom temperature, is well known.

In addition to requiring a pH-stable support material, a stable reversedphase also requires modifying the support material in order to provide astable, hydrophobic surface. Silylation is the most widely used methodto derivatize silica particles to produce hydrophobic reversed-phasesupports. The silylation of inorganic bodies other than silica (e.g.,alumina, titania, zirconia, etc.) has been disclosed in U.S. Pat. No.3,956,179. The hydrolytic instability of the siloxane bond is wellknown, and it is very likely that a Si-O-metal bond will be even moresusceptible to aqueous hydrolysis because of the increased polarity ofthe bond.

Another problem related to the use of silica-based reversed phasesupports is the difficulty encountered in the chromatography of aminesand other basic solutes. This problem results from the presence ofacidic silanol groups (SiOH) on the silica surface. Basic solutesundergo very strong interactions with these silanol groups which mayinvolve cation exchange or hydrogen bonding, depending on the pH of themobile phase. This problem is exaggerated by the requirement of workingin the range 2<pH<8 on silica-based columns, since most amines will beprotonated in this pH range and protonated amines can readily adsorb tothe silica surface. One approach to improving the chromatography ofamines is to work at hydrogen ion concentrations significantly above theionization constant of the amines so that they are unprotonated. Foraliphatic amines, this normally involves working at a pH greater than11. However, these pH ranges cannot be employed using silica-basedcolumns.

The presence of acidic silanol groups can also lead to irreversibleadsorption of many classes of organic molecules onto silica-basedreversed-phase supports, a problem which is well known in the art. Thisirreversible adsorption is particularly troublesome in thereversed-phase HPLC of proteins. Ultimately, this adsorption will resultin a change in the properties of the support and can lead to itsdestruction.

Mobile phase modifiers may be added to improve the chromatographicefficiency of basic compounds, but this can be expensive and hard onequipment. The resulting harsh conditions may cause irreversibleconformational and chemical changes in the compound of interest, as wellas contamination of compound to be purified.

E. Chemical Vapor Deposition

Chemical vapor deposition (CVD) is a vapor phase process wherein a solidmaterial is formed on a substrate by the thermal dissociation or thechemical reaction of one or more gas species. The deposited solidmaterial can be a metal, semiconductor, alloy, or refractory compound.

The use of CVD processes to produce carbon coatings has been extensivelystudied. Such processes are used, for example, to carbon coat nuclearmaterials or to infiltrate porous bodies so as to produce lightweightstructural materials. This topic is discussed in more detail in 9 TheChemistry and Physics of Carbon, 173-263 (P. Walker et al., eds. 1973),the disclosure of which is incorporated by reference herein.

F. Chromatographic Support Materials Having Polymeric Coatings

J. Knox et al., European Chromatography News, 1, 12-17 (1987) disclosethat graphite materials useful for liquid chromatography separations canbe modified by the adsorption of monolayers of high molecular weightmaterials, such as Tween 80 (polyethylene oxide sorbitol stearate). Themonolayer may be made insoluble in the eluent by cross-linking itin-situ. Knox et al. cite a personal communication of M. Wareing,Polymer Laboratories, Church Stretton, United Kingdom, which reports thecoating of porous graphitic carbon (PGC) with a thick layer of ahydrophilic polymer.

G. Schomburg, LC-GC, 6, 36 (1988) discloses that aluminas of suitableparticle geometry and pore structure can be polymer-coated bycross-linking an applied layer of polybutadiene having an averagemolecular weight of 4500. Schomburg further discloses a silica-basedsupport having a layer of poly(vinylpyrrolidone) (PVP) immobilized on asilica surface precoated by immobilization ofpoly(methyloctadecylsiloxane).

U Bien-Vogelsang et al., Chromatographia, 19, 170 (1984) disclosereversed-phase materials which were synthesized by polymer coatingsilica and alumina by in-situ generation of immobilized polymers usingthe various methods listed in Table VII at page 175.

ES Industries, Application News, ("γRP-1 HPLC Column" and "Comparison ofthe Chromegabond γRP-1 and γC18 Phases") (March, 1987) discloses γRP-1,an alumina based reverse phase packing material containing a polymercoating formed by means of cross-linking with γ-radiation.

H. Figge et al., J. Chromatography, 351, 393-408 (1986) discloseimmobilization methods involving either cross-linking and/or chemicalbonding of certain oligomers on unpretreated or premodified silicasurfaces.

Alpert (U.S. Pat. No. 4,517,241) discloses silica substrates which arederivatized by coating with polysuccinimide or polyaspartic acid inorder to provide a support material useful in cation exchangeseparations.

Tayot et al. (U.S. Pat. No. 4,673,734) discloses a mineral support ofsilica, alumina, magnesium, an oxide of titanium, or their natural orsynthetic derivatives, the porous surface of which has been coated withan aminated polysaccharide polymer. The polysaccharide polymer which isemployed to impregnate and cover the internal surface of the porousmineral support must be cationic and hydrophilic (Col. 2, lines 21-25).

Halasz et al. (U.S. Pat. No. 3,892,678) discloses porous silicon dioxidehaving substituted aliphatic or araliphatic amines with at least twocarbon atoms linked to the silicon dioxide surface by means of SiNbonds, wherein the linked radicals may be further altered bypolymerization. Modified silicon dioxides which contain unsaturatedradicals may react with other polymerizable compounds such as styrene,butadiene, vinyl compounds, acrylates, methacrylates, ethylene oxide,and propylene oxide.

SUMMARY OF THE INVENTION

The present invention provides a composite support material which isuseful as a stationary phase in liquid chromatography, particularly inhigh-performance liquid chromatography. The composite support materialcomprises carbon-clad particles of zirconium oxide (also referred toherein as ZrO₂, or as "zirconia"). In order to facilitate packing ofliquid chromatography columns, it is preferred that each individual unitof the present support material be a substantially spherical particle;thus, the preferred spherical particles will be referred to herein as"spherules." However, the present invention is also intended to providesupport materials useful in low performance chromatography, fluidizedbeds, and general batch absorbers. There is no requirement that thepresent particles be substantially spherical in these applications,where irregularly shaped particles are typically utilized.

Advantageously, the present carbon-clad ZrO₂ particles display very highphysical and chemical stability in aqueous media of high pH, e.g., pH14. At these conditions, the particles are substantially resistant todissolution of both the carbon cladding and the underlying ZrO₂, andprovide substantially constant solute retention during exposure toincreasing amounts of alkaline mobile phase.

Preferred carbon-clad ZrO₂ spherules useful for liquid chromatographyapplications will comprise a porous core ZrO₂ spherule. The corespherules will preferably have a diameter of about 1-500μ, morepreferably about 2-50μ; a surface area of about 5-300 m² /g, morepreferably about 15-100 m² /g; and a pore diameter of about 20-5000 Å,more preferably about 60-1000 Å.

In addition to the core ZrO₂ spherule, the support material of thepresent invention further comprises a cladding of carbon. As usedherein, the phrase "carbon-clad" means that an outer layer, sheath,coating, or cladding of pyrolytic carbon is bonded or otherwiseintegrally attached to the underlying ZrO₂ matrix. As used herein,"pyrolytic carbon" is intended to refer to carbon formed by thecarbonization of a suitable carbon source, e.g., a hydrocarbon."Carbonization" means that the hydrocarbon or other carbon source issubjected to conditions causing it to decompose into atomic carbon andother substances.

As mentioned above, the ZrO₂ cores of the present carbon-clad particlesare porous. When discussing porosity, the term "open pores" refers tointerior channels in the particles which exit at the surface of theparticle. The term "closed pores" refers to pores which have no exit atthe outside surface of the particle. The surface of closed pores areinaccessible to either gas or liquid phases with which the particles arecontacted. Thus, the closed pores are not affected by the claddingprocess, nor do they participate in subsequent use of the particles insurface active applications. As used herein, the term "pores" (or"porosity") refers to "open pores" only. By "surface of the particle",it is meant the exterior surface as well as the surface of the openpores. It is intended that the carbon cladding cover substantially allof the surface of the spherule, thus defined. As used herein,"substantially covering" or "substantially all" means that at leastabout 75%, preferably at least about 90%, and more preferably at leastabout 95% of the total surface area of the core ZrO₂ spherule will becovered by the carbon cladding.

Preferably, the thickness of the carbon cladding over the surface of theZrO₂ core ranges from the diameter of a single carbon atom (a monatomiclayer), to about 20 Å. This carbon cladding will thus not appreciablyincrease the diameter of the spherules. Thus, preferred carbon-clad ZrO₂spherules of the present invention will have a diameter of about 1-500microns and more preferably about 2-50μ. The carbon-clad ZrO₂ spheruleswill preferably have an average pore diameter of about 20-5000 Å, morepreferably about 60-1000 Å. The carbon-clad ZrO₂ spherules will alsopreferably have a surface area of about 5-300 m² /g, more preferablyabout 15-100 m² /g.

The scope of the present invention is also intended to encompasscarbon-clad ZrO₂ particles which are essentially non-porous. Prior tocarbon cladding, preferred non-porous ZrO₂ substrate particles will havea diameter of about 0.4-7 microns, a surface area of about 0.1-3 m² /g,and negligible internal porosity, although the particles may havesurface roughness. Useful non-porous ZrO₂ having the preferred diameterand surface area values can be prepared by methods well known to thoseof ordinary skill in the art of ceramic powder preparation. Thecarbon-clad non-porous particles are believed to be particularly usefulas a stationary phase support material in liquid chromatographyseparations of large molecules such as proteins and polymers. The sizeof such molecules can hinder or prohibit their rapid diffusion in andout of pores of a porous support material.

The present carbon-clad ZrO₂ particles may be used as an adsorbent;e.g., for gas or liquid purification. Further, the present carbon-cladZrO₂ particles can be formed into a bed, and employed as the stationaryphase in separations performed via chromatography, e.g., by gas, liquid,or super-critical fluid chromatography. Therefore, the particles can beused as the stationary phase in conventional chromatography columnswhich have an axial flow path, with or without rigid walls. For example,the particles, preferably spherules, can be packed into an HPLC column,where the packing functions as the stationary phase during HPLCseparations.

The carbon-clad particles of the present invention can also be combinedwith a suitable binder and used to coat a glass or plastic substrate toform plates for thin-layer chromatography.

In addition to their utility in chromatographic applications, thepresent carbon-clad ZrO₂ particles may be useful as an adsorptive mediumin non-chromatographic applications. For example, the particles may beutilized as an adsorptive medium in batch adsorbers, fluidized bedadsorbers, membrane adsorbers and the like. The particles may also beuseful as an adsorptive medium in pressure-swing adsorption apparatuses.In addition, the present particles may be useful as support materialsfor fixed bed reactors, batch reactors, fluidized bed reactors and thelike.

In addition to the carbon-clad ZrO₂ particles, the present inventionalso provides a method for forming a chromatographic support materialutilizing chemical vapor deposition. The method comprises the steps of:(a) placing a plurality of porous inorganic oxide particles having asurface within a reaction chamber; (b) establishing an elevatedtemperature within the reaction chamber, e.g., of about 500°-1500° C.;(c) establishing a reduced pressure within the reaction chamber, e.g.,of less than about 760 mm mercury; and (d) introducing a vaporcomprising carbon into the chamber so as to decompose the vapor anddeposit a cladding of the carbon onto the particles, substantiallycovering the surface of the particles. The present method may alsooptionally include an additional step (e) of exposing the carbon-cladparticles of step (d) to a gaseous reducing mixture comprising hydrogenso as to cause the reduction of polar functional groups on the surfaceof the particles. In this manner, a more homogeneous surface chemistrycan be achieved.

The present method is applicable to any inorganic oxide substrate towhich carbon will deposit under the operating conditions of the method.Useful inorganic oxides include, but are not limited to the Group II,III, and IV metals, i.e. HfO₂, ZrO₂, SiO₂, Al₂ O₃, TiO₂, and MgO.Preferably, a ZrO₂ or HfO₂ substrate is utilized in the present method,because the core ZrO₂ or HfO₂ particles maintain a useful surface areaat the high process temperatures (e.g., about 500°-1500° C.) which arepreferred for forming uniform CVD coatings. In contrast, the porousnetwork of alternative substrates, such as silica and alumina particles,may substantially degrade at these temperatures, with a resultingsurface area loss which may compromise the chromatographic character ofthese substrates. Furthermore, ZrO₂ or HfO₂ are especially preferredsubstrates because their high chemical stability means that exposure ofincompletely carbon-clad ZrO₂ or HfO₂ particles to aggressive mobilephases (e.g., pH 14), will not result in attack of the support witheventual dissolution. ZrO.sub. 2 is particularly preferred because it ismuch less expensive than HfO₂.

The present method for forming a chromatographic support materialutilizing chemical vapor deposition is intended to include a method forforming an essentially non-porous support material, such as thenon-porous carbon-clad ZrO₂ described above. When desired, step (a) ofthe method will comprise the step of placing a plurality of essentiallynon-porous inorganic oxide particles having a surface within a reactionchamber. The remaining steps (b) through (d) (and optionally step (e))of the method are not changed by the utilization of a non-poroussubstrate.

A preferred embodiment of the present invention is directed to apolymer-coated support material which is useful as a stationary phase inliquid chromatography applications. The support material preferablycomprises carbon-clad inorganic oxide particles which are coated with anoutermost layer of an organic polymer. The particles can be coated byadsorbing a polymerizable monomer or oligomer onto the surface of thecarbon-clad particles, and subsequently cross-linking the monomer oroligomer, e.g., by reaction with a free radical initiator or byirradiation. Useful inorganic oxides include, but are not limited to,the Group II, III and IV metals, i.e., HfO₂, ZrO₂, SiO₂, Al₂ O₃, TiO₂and MgO.

Although the inorganic oxide particles employed in the invention haveouter surfaces substantially covered with a carbon cladding as definedhereinabove, some inorganic oxide sites may remain exposed. Theseexposed sites may serve as sites for adsorption of oxygenated speciessuch as carbonates, sulfates, phosphates, and carboxylates. Suchadsorption may lead to inefficient chromatographic performance and poorpeak shape. The carbon cladding of these particles may also exhibitstrong interactions with certain species such as polar aromaticcompounds, further decreasing chromatographic efficiency. Moreover, thepresence of oxygenated sites on the carbon cladding can result in asurface which is energetically heterogenous, which in turn can cause aloss of chromatographic peak resolution.

The present preferred embodiment of the invention addresses theseproblems by employing a further polymeric coating over the carbon-cladsurface of the particles. Utilization of a non-polar polymeric coatingrenders the carbon-clad inorganic oxide particles substantiallyhydrophobic and provides a more energetically homogenous surface. Thepolymer coating ca improve the spectrum of properties of the support,e.g., loading and efficiency, without significantly altering any of itsdesirable physical and mechanical properties.

In the majority of reversed-phase liquid chromatography applications, ahydrophobic stationary phase material is required. Thus, hydrophobicpolymer-coated, carbon-clad particles according to the present inventionare a useful support for reversed phase liquid chromatography.Alternatively, the carbon-clad particles can be coated with ahydrophilic cross-linked polymer to form a support material useful forapplications of gas chromatography, supercritical fluid chromatography,solid phase extraction, fluidized beds, and the like. These hydrophilicpolymer coatings are formed from monomers or oligomers which comprisepolar groups such as sulfonic acids, carboxylic acids, amino groups,phenolic groups, or quaternary ammonium groups. A preferred method toprepare such a coating comprises sorbing a polymerizable monomer oroligomer onto the surface of the spherules, and cross-linking themonomer or oligomer. See G. Schomberg, LC-GC, 6, 36 (1988).

The present polymer-coated particles can also be combined with asuitable binder and used to coat a glass or plastic substrate to formplates for thin-layer chromatography.

In addition to their utility in chromatographic applications, thepresent polymer-coated carbon-clad inorganic oxide particles may beuseful as an adsorptive medium in non-chromatographic applications. Forexample, the particles may be utilized as an adsorptive medium in batchadsorbers, fluidized bed adsorbers, membrane adsorbers and the like. Theparticles may also be useful as an adsorptive medium in pressure-swingadsorption apparatuses. In addition, the present particles may be usefulas support materials for fixed bed reactors, batch reactors, fluidizedbed reactors and the like.

Therefore, a preferred embodiment of the present invention is achromatographic support material comprising carbon-clad inorganic oxideparticles having a cross-linked outermost coating of a polymer thereon,wherein the polymer-coated particles preferably have a pore size fromabout 50-1000 Å, a surface area of about 2-80 m² /g, and an averagediameter of about 2-1000μ. As used herein, "polymer coating" means thatthe carbon-clad surface of the particle is substantially covered with alayer of an organic polymer. Preferred embodiments of the particles willcomprise about 0.1-10 mg polymer per square meter of the surface of thecarbon-clad particles. Since spherically shaped particles are desirablefor packing into liquid chromatography columns, a preferred embodimentof the present polymer-coated support material comprises substantiallyspherical particles, or "spherules."

The scope of the present invention is also intended to encompasspolymer-coated, carbon-clad ZrO₂ particles which are essentiallynon-porous. Prior to carbon cladding, preferred non-porous inorganicoxide substrate particles will have a diameter of about 0.4-7 microns, asurface area of about 0.1-3 m² /g, and negligible internal porosity,although the particles may have surface roughness. Useful non-porousinorganic oxides having the preferred diameter and surface area valuescan be prepared by methods well known to those of ordinary skill in theart of ceramic powder preparation. The polymer-coated, carbon-cladnon-porous particles are believed to be particularly useful as astationary phase support material in liquid chromatography separationsof large molecules such as proteins and polymers. The large size of suchmolecules can hinder or prohibit their rapid diffusion in and out ofpores of a porous support material.

Advantageously, the present polymer-coated, carbon-clad support materialdisplays a remarkable stability over a wide pH range, and can be usedfor the chromatographic separation of compounds at their optimal pHs.For example, the carbon-clad, polymer-coated material prepared accordingto the invention can be used for the separation of amines at a varietyof pHs and mobile phase conditions so that the separation occurs eitherby a reversed-phase retention mode, a cation-exchange mode, or somecombination of the two. For example, at high pH (e.g., pH=12), theamines are unprotonated so that separation occurs entirely by areversed-phase mode. At low pH, in the presence of a low ionic strengthphosphate buffer and with an organic solvent-rich mobile phase, theseparation can occur via a cation-exchange mode if the polymer coatingcontains cation exchange groups, e.g., carboxylic or sulphonic acidgroups. By adjustment of mobile-phase conditions, selectivity can thusbe significantly enhanced.

Another advantage of the present polymer-coated, carbon-clad material isthat various desired surface chemistries can be imparted to the materialby the cross-linking of a variety of polymers on the carbon-clad surfaceand, optionally, chemical derivatization of the polymeric coating. Inthis manner, stationary phase supports for reversed phasechromatography, hydrophobic interaction chromatography, size exclusionchromatography, affinity chromatography, chiral chromatography and ionexchange chromatography can be realized. The table below listsrepresentative polymer coatings which are suitable for various desiredchromatographic characters.

    ______________________________________                                        Polymer Chemistries for Different Chromatographic Characters                  Desired          Recommended                                                  Chromatographic Character                                                                      Polymer Coating                                              ______________________________________                                        Reversed Phase   Polybutadiene                                                                 C.sub.18 -C Derivatized Polymer                                               Polystyrene                                                  Hydrophobic Interaction                                                                        Polyvinylalcohol                                                              Poly(ethylene glycol)                                                         Polyvinylpyrollidone                                         Ion Exchange     Polyethyleneimine                                                             Poly(butadiene maleic acid)                                  Size Exclusion   Dextran                                                                       Polyvinylpyrollidone                                                          Polyvinylalcohol                                                              Polysiloxanes                                                Affinity         Affinity Ligands Attached to                                                  N-Acryloxysuccinimide                                        Chiral           Poly-l-Histidine                                             ______________________________________                                    

The present invention further provides a method for forming apolymer-coated support material useful as a stationary phase in liquidchromatography. The method includes the steps of (a) providing aplurality of inorganic oxide particles comprising a surface which issubstantially covered by a carbon cladding; (b) coating the carbon-cladparticles with a monomer or oligomer; and (c) cross-linking the monomeror oligomer to form a plurality of polymer-coated, carbon-cladparticles. In a preferred application, the method includes an additionalstep of exposing the carbon-clad particles to a gaseous reducing mixturecomprising hydrogen prior to coating them with the monomer or oligomer.This exposure is intended to cause reduction of polar oxygenated siteswhich may remain exposed on the particles' surfaces following theapplication of the carbon layer. The carbon-clad inorganic oxideparticles to be polymer coated in application of the present method mayhave a porous surface or may be essentially non-porous.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows apparatus including a reaction chamber within a small tubechamber.

FIG. 2A shows a chromatogram of a mixture of alkylbenzenes.

FIG. 2B shows a chromatogram of a mixture of alkylphenones.

FIG. 3 depicts a plot of logarithm of the capacity factor k' vs. carbonnumber of the components of the alkylbenzene mixture (ethylbenzenethrough hexylbenzene) and the components of alkylphenone mixture(acetophenone through hexanophenone).

FIG. 4 shows a stability study.

FIGS. 5, 6, and 7 depict plots of log(capacity factor) vs. carbon numberfor each alkylphenone component and alkylbenzene components of amixture.

FIGS. 8A and 8B show flow rate studies.

FIGS. 9A, 9B, and 10 show loading studies.

FIG. 11 depicts a chromatogram of a mixture of alkylphenones separatedby carbon-clad, polybutadiene spherules.

FIG. 12 is a schematic depiction of a porous polymer-coated, carbon-cladZrO₂ particle of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides both a composite material useful as achromatographic support, and a method for forming a chromatographicsupport material.

The present material comprises a particle, preferably a sphericalparticle or "spherule", comprising a core, base or substrate of a porouszirconium oxide, and a cladding of carbon over the porous core. Becausean intended use of the present support material is in liquidchromatography applications, it is preferred that the individual unitsof the material be spherical in shape, in order to permit optimalpacking into a column. Therefore, as used herein with respect to thepresent support material, a "spherule" refers to a substantiallyspherical particle. Accordingly, as used herein, a "diameter" of a unitof the present support material refers to the average lateral dimensionor "particle size" across the particle, but is not intended to implythat the particle is a perfect sphere. The words "spherule" and"particle" are intended to be used interchangeably hereinafter, as arethe words "diameter," "size" and "particle size." The present inventionis also intended to encompass irregularly shaped particles, which may beuseful, e.g., in low performance chromatography, fluidized beds, andgeneral batch absorbers.

The diameter of the core ZrO₂ particles may vary within rangesappropriate for the desired use of the particles. Generally in sorbentapplications, ZrO₂ particles of up to about 1 cm in size are preferred.For liquid chromatography applications, preferred core ZrO₂ spherulesrange in size from about 1-500μ, and more preferably, about 2-50μ.

The criteria for utility of a particular material as the core orsubstrate of the present carbon-clad particles are that the basematerial, preferably in the form of a spherule, possesses a high totalsurface area and thus good sorption capacity, and that this surface areais not excessively reduced during the carbon cladding and any othersubsequent coating or cladding procedure included within the scope ofthe present invention. Therefore, useful surface areas for the core ZrO₂particles range from about 5-300 m² /g, more preferably about 15-100 m²/g.

The present carbon-clad ZrO₂ particles are preferably prepared by a lowpressure chemical vapor deposition (CVD) method, discussed below, whichmethod is also included within the scope of the present invention.Therefore, the pore diameter of the base material must be sufficientlylarge to permit ready diffusion of hydrocarbon vapor into the pores ofthe core ZrO₂ particle during the CVD. Thus, preferred pore sizes forthe core ZrO₂ particles range from about 20-5000 Å, more preferablyabout 60-1000 Å.

The present zirconium oxide cores are clad or coated with a layer ofpyrolytic carbon. Terms related to carbon and its formation arediscussed and defined in 9 The Chemistry and Physics of Carbon 173-263(P. Walker et al., eds. 1973), the disclosure of which is incorporatedby reference herein. For example, at pages 174-175, the authors disclosethat "pyrolytic carbon" and "CVD carbon" are generic terms relating tothe carbon material that is deposited on the substrate by the thermalpyrolysis of a carbon-bearing vapor. The term "CVD carbon" describes theprocessing used, whereas the term "pyrolytic carbon" refers more to thetype of carbon material that is deposited. The authors further disclosethat the process of depositing pyrolytic carbon in porous substrates isgenerally referred to as "infiltration."

While any method of applying pyrolytic carbon to a porous substrate canbe used in the preparation of the present carbon-clad zirconia, it ispreferable to apply the carbon cladding in a manner which results insubstantial carbon coverage of the porous ZrO₂ surface. Our method,detailed below, employs a low pressure chemical vapor depositiontechnique to substantially clad a porous inorganic oxide particle. Forexample, by utilizing the present method, a carbon cladding can beapplied which covers greater than 98% of the total exposed surface of aporous zirconia particle, within a time period of about 30 minutes andat a deposition temperature of about 700° C., when toluene is used asthe carbon source.

The present carbon-clad ZrO₂ support material is useful in at least twofields:

First, the present carbon-clad ZrO₂ material is useful as a stablereversed-phase chromatographic support material. Advantageously, theselectivity for polarizable solutes and hydroxyl solutes can beexploited to separate these species. The loading capacity of the supportfor these species can be adjusted, if required, by proper selection ofthe support material (i.e., pore size and specific surface area) andcolumn size (overall capacity).

Second, the carbon cladding is useful as a covering or masking agent forthe ZrO₂ surface. ZrO₂ surfaces are known to interact strongly withcarboxylic acids, sulfonates, phosphates, and the like. Theseinteractions can lead to undesirable behaviors in chromatographyapplications. Although some residual ZrO₂ sites may still remain exposedafter the carbon cladding, substantially all of the surface is coveredwith a carbon cladding whose retentivity can be controlled more easilythan the retentivity of bare ZrO₂. Improvement of the coating and/oroptimization of the pore geometry together with this technology may beused to produce a uniform hydrophobic coating to "seal" the ZrO₂surface.

There is significant solvent selectivity involved in the use of thepresent carbon-clad ZrO₂ for chromatography. The choice of solvent mayalso affect the level of solute loading which can be practicallyemployed.

I. Sources of Zirconium Oxide

In a preferred embodiment of the present carbon-clad ZrO₂ particles, thecore ZrO₂ particles will be spherules formed from a ZrO₂ sol. In thisembodiment, a portion, or more preferably a majority, of the initialZrO₂ used to form the core spherules will be in the sol state; i.e., acolloidal dispersion of ZrO₂ particles in water. Once the water isremoved, the sol particles interact strongly with one another to provideaggregated sol particles.

Colloidal dispersions of zirconium oxide suitable for use as the ZrO₂source in preparation of the present spherules include the Nyacol™ Zrseries, Nyacol, Inc., Ashland, Mass. These dispersions contain about 20wt-% ZrO₂, wherein the ZrO₂ particles vary in average diameter, e.g.,from about 10-200 nm. For example, Nyacol™ Zr 100/20 is an aqueousdispersion containing 20 wt-% ZrO₂ of colloidal ZrO₂ particles, themajority of which are about 100 nm in diameter.

Non-colloidal ZrO₂ sources may be included along with the colloidal ZrO₂dispersions as useful starting materials for these spherules. Thus,chloride, nitrate, sulphate, acetate, formate or other inorganic ororganic salts of zirconium such as the oxysalts and alkoxides may beincluded with the ZrO₂ sol and the mixture used to make spherules.Preferably, colloidal ZrO₂ particles make up the major portion of thetotal ZrO₂ present in the mixture.

Organic compounds may also be included with the ZrO₂ sources used toprepare the spherules. These organic materials are removed during thefiring of the spherules. In particular, water-soluble polymers such aspolyvinylpyrrolidone, polyethylene glycol, polyethylene oxide, and thelike, or latex particles may be included in the liquid mixture used toprepare the spherules. These materials may act to alter the rheology ofthe precursor solution, or the pore structure of the resulting firedspherule.

The core ZrO₂ spherules can comprise a minor amount of other metaloxides in addition to ZrO₂. For example, precursors for other metaloxides may be included with the ZrO₂ precursors, so as to stabilize aparticular crystalline phase of ZrO₂ or to retard grain growth in thefired spherules. Thus, salts or sols of metals such as yttrium,magnesium, calcium, cerium, aluminum, and the like may be included inlevels of from approximately 0-20 mole-%. ZrO₂ spherules which do notcontain other oxide additives and are fired in air or in oxidizingatmospheres display either monoclinic, tetragonal or pseudocubic crystalstructures when cooled to room temperature. Higher firing temperaturesand longer firing times favor the formation of the monoclinic phase. Theinclusion of other metal oxides allows the preparation of spheruleswhich possess either monoclinic, tetragonal, or cubic crystallinestructures.

These features of ZrO₂ are well known in the art and are discussed in,for example, An Introduction to Zirconia, Magnesium Elektron Ltd.,Twickenham, England (2d ed., Magnesium Elektron Publication No. 113,July 1986).

II Preparation of Core ZrO₂ Spherules

In preferred embodiments wherein the core zirconium oxide spherules areto be formed from a ZrO₂ sol, an aqueous sol containing a colloidaldispersion of ZrO₂ particles can be dispersed in a medium which willextract water from the dispersed sol in the form of droplets. Removal ofall or a portion of the water results in gelled solid spherules whichconsist of aggregated sol particles. One extracting medium which may beused is 2-ethyl-1-hexanol, as disclosed in U.S. Pat. No. 4,138,336. Apreferred extracting medium for safety reasons and ease of processing ispeanut oil, which is preferably used at a temperature of about 80°-100°C. The most preferred extracting medium is a mixture of peanut oil andoleyl alcohol, which are combined in a ratio of about 1:1 and used at atemperature of about 80-100° C. Oleyl alcohol possesses a higherextraction capacity than peanut oil, and mixtures of the two allow theextraction capacity of the medium to be controlled. Depending upon theratio of sol to forming medium, extraction times of from about 1-60minutes can be used to fully gel the ZrO₂ particles. The gelledspherules may be conveniently separated from the extracting medium byany suitable method, e.g., by filtration.

The spherules may also be prepared by the process of spray drying, asdisclosed, for example, in U.S. Pat. No. 4,138,336.

Once the ZrO₂ particles are condensed into spherules in the abovemanner, thermal treatment at firing temperatures of from about100°-1500° C., preferably about 400°-800° C., is performed. Theresulting fired spherules are preferably from about 1-500μ in diameter,and preferably possess a surface area of 5-300 m² /g and pore diametersof about 20-5000 Å.

III. Low Pressure CVD Method

The present invention also encompasses a method for forming achromatographic support material utilizing chemical vapor deposition atlow pressure. Either porous or essentially non-porous inorganic oxidespherules can be employed as the substrate material. Advantageously,both the interior and the exterior surfaces and the surfaces of any openpores of the inorganic oxide substrates treated in accordance with thepresent method can be substantially covered with a cladding of carbon.By "low pressure," it is meant that the pressure of the vaporized carbonsource in the deposition chamber will be preferably less than about 50Torr, and more preferably less than about 20 Torr. Since the systempressure in the deposition chamber prior to introduction of thevaporized carbon source will preferably be less than about 10 Torr, thetotal pressure during the deposition will preferably be less than about60 Torr, and more preferably less than about 30 Torr.

The preferred temperature to be maintained during deposition of carbonaccording to the present method ranges from about 500°-1500° C., andmore preferably is about 600°-1000° C. The preferred deposition time isfrom about 1 minute-4 hours (240 minutes), but more preferably isbetween 15 minutes-1 hour. It is believed that the present methodadvantageously provides inorganic oxide spherules with a much morecomplete and uniform surface coverage in a shorter period of time thanconventional CVD techniques.

The inorganic oxide spherules which are preferably utilized in thepresent method will have a diameter of about 1-500 microns, a surfacearea of about 5-300 m² /g, and, if porous, a pore diameter of about20-5000 Å. Although any inorganic oxide meeting these criteria may beemployed as a core or substrate material in practice of the presentmethod, preferred inorganic oxides include those commonly employed insorbent applications, e.g., SiO₂, TiO₂, Al₂ O₃, MgO, and ZrO₂. SuitableSiO₂ spherules are commercially available under the trade name HPLCSilica Nucleosil, from Macherey-Nagel (Germany). For liquidchromatography applications, a metal oxide which displays a relativelyhigh resistance to dissolution in aqueous media is preferably employed.Suitable metal oxides in this group include, but are not limited to, Al₂O₃, TiO₂, HfO₂ or ZrO₂, with ZrO₂ and HfO₂ being most preferred metaloxides because of their high resistance to dissolution. Suitable Al₂ O₃spherules are commercially available under the trade name SpherisorbAlumina from Phase Sep, Inc., Hauppauge, N.Y. Suitable TiO₂ spherulescan be prepared as disclosed in U.S. Pat. No. 4,138,336. Compounds ormixtures of more than one inorganic oxide may also be employed in thepresent method as the core or substrate material.

Any carbon source which can be vaporized and which will carbonize on thesurface of the inorganic oxide substrate under the temperature andpressure of the present method may be employed to deposit a carboncladding via CVD. Useful carbon sources include hydrocarbons such asaromatic hydrocarbons, e.g., benzene, toluene, xylene, and the like;aliphatic hydrocarbons, e.g., heptane, cyclohexane, substitutedcyclohexane butane, propane, methane, and the like; unsaturatedhydrocarbons; branched hydrocarbons (both saturated and unsaturated),e.g., isooctane; ethers; ketones; aldehydes; alcohols such as heptanol,butanol, propanol, and the like; chlorinated hydrocarbons, e.g.,methylene chloride, chloroform, trichloroethylene, and the like; andmixtures thereof. Another useful carbon source may be a gaseous mixturecomprising hydrogen and carbon monoxide, as described by P. Winslow andA. T. Bell, J. Catalysis, 86, 158-172 (1984), the disclosure of which isincorporated by reference herein.

The carbon source may be either a liquid or a vapor at room temperatureand atmospheric pressure although it is employed in the CVD process invapor form. If the carbon source is a liquid with low volatility at roomtemperature, it may be heated to produce sufficient vapor for thedeposition.

In general, the choice of the optimum deposition temperature, pressureand time conditions are dependent on the carbon source employed and thenature of the metal oxide. For example, higher hydrocarbon vaporpressures, higher deposition temperatures and longer deposition timeswill generally lead to increased amounts of carbon being deposited.Higher deposition temperatures and higher total pressures will, however,also result in a greater tendency for deposition to be localized on ornear to the peripheral surface of the substrate particles. If suchincreased deposition on the exterior surface restricts access of thehydrocarbon vapor to the surfaces of the pores of the particle, theseinternal surfaces may be poorly coated and therefore theirchromatographic performance impaired. Furthermore, the restricted accessto the pores may also reduce the chromatographic utility of theparticle. Thus, it is preferable to optimize deposition conditions sothat the carbon cladding substantially and evenly covers both theexternal surface and the surfaces of the pores, and does not restrictthe subsequent access of hydrocarbon to the surface of the pores. Thiscondition is favored by lower deposition temperatures, e.g., 500°-1000°C. and lower total pressures, e.g., 1-50 Torr. Since lower depositiontemperature and pressure results in a slower rate of carbon deposition,longer deposition times will be employed in order to deposit a layer ofcarbon adequate to cover the surface of the particle. Therefore, theoptimum conditions may require a compromise between degree of surfacecoating and length of deposition time. Advantageously, the presentmethod results in substantially complete surface coverage of theinorganic oxide spherules, i.e., at least about 75%, preferably at leastabout 90%, and more preferably at least about 95% of the surface will becovered.

A suitable apparatus for carrying out the present method utilizingchemical vapor deposition is shown schematically in FIG. 1 by referencenumeral 10. In an application of the present method, a sample 12 ofinorganic oxide spherules is placed in sample boat 14, and centrallypositioned within a tubular reaction chamber 16 (cross-section notshown). Tubular reaction chamber 16 is situated substantiallycocentrically within tubular furnace 18, which has a first end 20 and asecond end 22. Tubular furnace 18 also includes means for maintainingthe sufficiently high temperature, e.g., 500°-1500° C., within thetubular furnace, for chemical vapor deposition.

Connected to both first end 20 and second end 22 of tubular reactionchamber 16 are end fittings 24. The end fitting 24 connected to secondend 22 is an "O"-ring joint which provides means for connecting secondend 22 to a winch 26, while end fitting 24 connected to first end 20 oftubular reaction chamber 16 is an "O"-ring joint which provides meansfor connecting first end 20 to an inner quartz tube 28. After chemicalvapor deposition is completed, sample 12 in sample boat 14 may beremoved from reaction chamber 16 without breaking a vacuum seal by meansof an arrangement consisting of a temperature-resistant thread 32connected to winch 26.

The pressure within tubular reaction chamber 16 can be reduced to belowatmospheric pressure by means of vacuum system, shown generally asreference numeral 30. The pressure may be measured by vacuum sensor 40and indicated by vacuum gauge 42, or by any other suitable means. Inmore sophisticated apparatuses, it is envisioned that a feedback controlsystem could receive an input signal from vacuum sensor 40 and wouldcontrol pressure by adjusting the vacuum pump operation accordingly.Additionally, means of monitoring the flow of vapor into the reactionchamber would be provided. Preferably, means for agitating the sample ofspherules during the deposition process would be provided to ensure morethorough coating uniformity.

Inner quartz tube 28 is connected to vacuum tubing 34 which is in turnconnected to a flask 36 containing a carbon source 38. The temperatureof carbon source 38 is maintained by a water bath in which flask 36 isimmersed or by other suitable means known in the art. It is preferredthat the carbon source 38 and the water of the water bath are bothstirred to maintain a constant temperature. Carbon source vapor iscarried through vacuum tubing 34 and inner quartz tube 28 into reactionchamber 16, where it decomposes upon contact with sample 12 maintainedat an elevated temperature, e.g., 500°-1500° C., within the reactionchamber. Thus, a thin cladding of carbon is deposited on the surface ofthe porous inorganic oxide spherules of sample 12.

After their preparation according to the present method, the carbon-cladspherules may be packed into a chromatography column and used to performliquid chromatographic separations. Conventional slurry packingtechniques can be employed to pack LC columns with the spherules. For ageneral discussion of LC techniques and apparatuses, see Remington'sPharmaceutical Sciences, A. Osol, ed., Mack Publishing Col, Easton, Pa.(16th ed..1980), at pages 575-576, the disclosure of which isincorporated by reference herein.

IV. Polymer-Coated Carbon-clad Inorganic Oxide Particles

A. Polymerizable Monomers or Oligomers

A wide variety of cross-linkable organic materials, which may bemonomers, oligomers or polymers, can be employed to coat the carbon-cladinorganic oxide particles of the present invention. For example, suchmaterials include polybutadiene, polystyrene, polyacrylates,polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA),polyorganosiloxanes, polyethylene, poly(C₁ -C₄)alkylstyrene,polyisoprene, polyethyleneimine, and polyaspartic acid.

A preferred material for the preparation of a reversed-phase supportmaterial is the oligomer precursor of a hydrophobic polymer such aspolybutadiene. A preferred material for modification of the spherules toform a cation ion exchange support is polyaspartic acid.

B. Cross-linking Agents

Any of the common free radical sources including organic peroxides suchas dicumyl peroxide, benzoyl peroxide or diazo compounds such as2,2'-azobisisobutyronitrile (AIBN) may be employed as cross-linkingagents in the practice of the present invention. Useful commerciallyavailable peroxyesters include the alkylesters of peroxycarboxylicacids, the alkylesters of monoperoxydicarboxylic acids, thedialkylesters of diperoxydicarboxylic acids, the alkylesters ofmonoperoxycarbonic acids and the alkylene diesters of peroxycarboxylicacids. These peroxyesters include t-butyl peroctoate, t-butylperbenzoate, t-butyl peroxyneodecanoate and t-butyl peroxymaleic acid.These compounds are commercially available from Pennwalt Chemicals,Buffalo, N.Y. The amount of any free radical initiator required tocatalyze the polymerization reaction will vary depending upon themolecular weight of the initiator and its thermal stability. For typicalapplications of the present invention, about 2-2.5 g of initiator willbe required per 100 g pre-polymer.

Oligomers may also be polymerized by irradiation with UV light or gammarays or by exposure to high energy electrons.

C. Polymer Coating/Cross-linking Process

Once inorganic oxide spherules have been carbon-clad, the chemicalcharacter of the particles (Reversed Phase, Ion Exchange, etc.) can becontrolled by coating the particles with a selected pre-polymer. Thepolymeric coating is generally performed in two steps. First, apre-polymer is deposited on the surface of the carbon-clad particle.Secondly, the pre-polymer is immobilized by a cross-linking reaction,thereby creating a continuous polymeric coating on the surface of theparticle.

The pre-polymer can be deposited on the particle surface in a variety ofways, including pre-polymer deposition by solvent removal, selectiveadsorption from solution, and gas phase deposition.

When chemical cross-linking agents are used, the cross-linking reactionis preferably carried out under vacuum, to inhibit oxidation of thepre-polymer or polymer. Alternatively, the cross-linking reaction can becarried out in an inert gas, such as nitrogen or helium.

After cooling under a vacuum and rinsing with solvent to remove residualpre-polymer, the resultant polymer-coated particles can be packed intoHPLC columns by dry packing or upward slurry packing, depending on theirparticle size.

The invention will be further described by reference to the followingdetailed Examples. The examples are directed to the following subjectmatter:

    ______________________________________                                        Examples 1-8  Preparation of Core ZrO.sub.2                                                 Spherules                                                       Examples 9-17 Carbon Cladding by Low Pressure                                               CVD Method                                                      Examples 18-19                                                                              Chromatographic Studies                                                       Utilizing Carbon-Clad ZrO.sub.2 as                                            Stationary Phase                                                Examples 20-23                                                                              Chromatographic Studies                                                       Comparing Silica and Carbon-Clad                                              ZrO.sub.2 Stationary Phases                                     Example 24    Comparison of Aromatic and                                                    Aliphatic Hydrocarbon Carbon                                                  Sources for CVD                                                 Example 25    Comparison of Alcohol and                                                     Aliphatic Hydrocarbon Carbon                                                  Sources for CVD                                                 Examples 26-27                                                                              Preparation and Evaluation of                                                 Polybutadiene-Coated Carbon-Clad                                              ZrO.sub.2 Spherules                                             ______________________________________                                    

EXAMPLE 1 Preparation of Core ZrO₂ Spherules

Peanut oil (3 liters) was placed in a 4 liter beaker and heated to 90°C. A mechanical agitator was inserted and the peanut oil was vigorouslystirred. One hundred grams of Nyacol™ Zr 95/20, a colloidal ZrO₂manufactured by Nyacol, Ashland, Mass., and containing 20 wt-% of ZrO₂,primarily as about 95 nm particles, was sprayed into the peanut oilthrough an aerosol atomizer. After approximately 30 minutes, the batchwas filtered through a No. 54 Whatman filter. Approximately 17 g ofsolids were recovered, which were predominately spherules having adiameter of <30μ.

EXAMPLE 2 2 Preparation of Core ZrO₂ Spherules

Peanut oil (600 g) and 600 g of oleyl alcohol were mixed and heated toabout 90° C. Under vigorous agitation, 100 g of Nyacol™ Zr 95/20 wassprayed into the peanut oil/oleyl alcohol mixture as described inExample 1. After 30 minutes, the batch was filtered and the particlescollected. The particles were predominately (ca: 70%) spherules having adiameter of <50μ.

Spherules prepared as described in Examples 1 and 2 were thermallytreated at a series of temperatures and the surface area, average porediameter and pore volume as a percentage of total volume were measuredby nitrogen adsorption isotherm on a Quantasorb surface area analyzer.These results are summarized in Table 2-1, below.

                  TABLE 2-1                                                       ______________________________________                                        Physical Characteristics of ZrO.sub.2 Spherules                               Firing   Surface     Average Pore                                                                              Pore                                         Temp (°C.)*                                                                     Area (m.sup.2 /g)                                                                         Diameter (Å)                                                                          Volume (%)                                   ______________________________________                                        400      142          42         47                                           500      92           71         50                                           600      34          110         36                                           800      17          205         34                                           900      14          220         31                                           ______________________________________                                         *6 hrs                                                                   

The data summarized in Table 2-1 show that it is possible to increasethe average pore diameter by increasing the firing temperature from 400°to 900° C. The surface area and pore volume decrease with increasingfiring temperature. Since chromatographic capacity of the ZrO₂ spherulesis determined by the surface area, average pore diameter and porevolume, the appropriate firing temperature can be selected to controlthese parameters.

EXAMPLE 3 Preparation of Core ZrO₂ Spherules

The procedure of Example 2 was employed to prepare spherules usingNyacol™ Zr 50/20, a colloidal ZrO₂ supplied by Nyacol, Inc. (50 nm ZrO₂colloidal size) as the ZrO₂ source.

EXAMPLE 4 Preparation of Core ZrO₂ Spherules

The procedure of Example 2 was used to prepare spherules using Nyacol™Zr 150/20, a colloidal ZrO₂ supplied by Nyacol, Inc. (150 nm ZrO₂colloid size) as the ZrO₂ source.

Table 4-1 summarizes the surface area, average pore diameter and porevolume of spherules prepared as per Examples 2-4 and fired at 600° C.for 6 hrs.

                  TABLE 4-1                                                       ______________________________________                                        Physical Characteristics of ZrO.sub.2 Spherules                                       ZrO.sub.2                                                                     Colloid                      Pore                                     ZrO.sub.2                                                                             Size    Surface    Average Pore                                                                            Volume                                   Source* (nm)    Area (m.sup.2 /g)                                                                        Diameter (Å)                                                                        (%)                                      ______________________________________                                        Zr 50/20                                                                              50      33          92       31                                       Zr 95/20                                                                              95      34         110       36                                       Zr 150/20                                                                             150     40         147       45                                       ______________________________________                                         *Nyacol ™ series.                                                     

The data summarized in Table 4-1 show that it is possible to control theaverage pore diameter of the fired spherules by appropriate selection ofthe colloid size of the ZrO₂ source. Larger colloids produce firedspherules with larger pore diameters and pore volumes.

EXAMPLE 5 Preparation of Core ZrO₂ Spherules with Single Centrifugation

Nyacol™ Zr 95/20 colloidal ZrO₂ was placed in a laboratory centrifugeand sedimented. The supernatant was decanted and discarded. Thesedimented ZrO₂ was redispersed in an equal volume of distilled water.Spherules were prepared from this centrifuged sol following theprocedures of Example 2.

EXAMPLE 6 Preparation of Core ZrO₂ Spherules with Double Centrifugation

The centrifugation procedure of Example 5 was performed and theredispersed sol was subsequently recentrifuged to sediment, thesupernatant decanted off and the ZrO₂ redispersed. Spherules wereprepared from this doubly centrifuged sol following the procedure ofExample 2.

EXAMPLE 7 Preparation of Core ZrO₂ Spherules with Triple Centrifugation

The double centrifugation procedure used in Example 6 was performed andthe redispersed sol was subsequently recentrifuged to sediment, thesupernatant decanted and the ZrO₂ redispersed. Spherules were preparedfrom this triply centrifuged sol following the procedures of Example 2.

Table 7-1 summarizes the surface area, pore diameter and pore volume ofspherules prepared as per Examples 2, 5, 6 and 7 and heated to 600° C.for 6 hrs.

                  TABLE 7-1                                                       ______________________________________                                        Physical Characteristics of ZrO.sub.2 Spherules                               ZrO.sub.2   Surface    Average Pore                                                                            Pore                                         Source*     Area (m.sup.2 /g)                                                                        Diameter (Å)                                                                        Volume (%)                                   ______________________________________                                        Zr 95/20    34         110       36                                           Zr 95/20 cent. (1x)                                                                       50         162       55                                           Zr 95/20 cent. (2x)                                                                       52         235       62                                           Zr 95/20 cent. (3x)                                                                       46         250       62                                           ______________________________________                                         *Nyacol ™ Zr series.                                                  

Centrifugation, removal of the supernatant, and redispersion of thecolloidal ZrO₂ starting material results in increases in the averagepore diameter, pore volume and surface area of fired spherules. Thisincrease is believed to result from the removal of small (ca. 5-10 nm)colloidal ZrO₂ particles which are known to be present in the Nyacol™ Zrseries sols as a minor component. Many of these smaller ZrO₂ particlesremain suspended during centrifugation and are removed when thesupernatant is discarded prior to redispersion of the larger sedimentedZrO₂ particles. If present, these small ZrO₂ particles are believed toincrease the packing density of the spherules by filling the intersticesbetween larger ZrO₂ particles and therefore decreasing the average porediameter, pore volume and surface area of the fired spherules.

It is also possible that sedimentation by centrifugation may result inagglomeration of the colloidal ZrO₂ particles into aggregates which packtogether in a more open structure (effectively behaving as largerparticles) than unaggregated particles.

Regardless of mechanism, the centrifugation treatments described inExamples 5-7 provide a method of preparing spherules with increasedaverage pore diameter, pore volume and surface area relative tospherules prepared from untreated colloidal ZrO₂ sols.

EXAMPLE 8 Preparation of Core ZrO₂ Spherules With Spray Drying

Preparation A

A 4500 g sample of Nyacol™ Zr 100/20, which contained 20 wt-% ZrO₂primarily as about 100 nm particles, was concentrated on a rotaryevaporator until its concentration was 35% ZrO₂ by weight. This sol wasthen spray dried on a spray drier manufactured by Nyro Incorporated.About 900 g of dried solids were obtained. When examined under anoptical microscope, the solids were observed to be spherules from about0.5 to 30μ in diameter. The dried spherules were fired by heating themin a furnace to a temperature of 600° C. over 6 hours, with additionalheating applied at a constant temperature of 600° C. for 6 more hours.Nitrogen adsorption measurements on the fired ZrO₂ spherules indicatedthat their average surface area was 48.1 m² /g and their average porediameter was 116 Å. The spherules were air classified, and the fractionranging in size from approximately 5-10μ was subsequently used forchromatography experiments.

Preparation B

To prepare spherules with larger diameter pores than those ofPreparation A, the procedure described below was followed. 1200 g ofNyacol™ Zr 100/20 colloidal ZrO₂ were centrifuged on a laboratorycentrifuge at 5000 rpm for 55 minutes. The supernatant was discarded andthe sediment was re-dispersed in distilled water. The centrifuged solwas placed on a rotary evaporator and concentrated until it contained35% by weight of ZrO₂. Following spray drying of the sol underconditions similar to those described in Preparation A, about 300 g ofdried solids were obtained. When examined under an optical microscope,the solids were observed to be spherules ranging in size from about 1 to30μ in diameter. Many of the spherules (>50%) were observed to possesscracks, especially those spherules of larger size.

A portion of the fired spherules was then placed in a furnace and heatedto a temperature of 1100° C. over 9 hours, with additional heating at aconstant temperature of 1100° C. for 6 more hours. The surface area ofthe fired spherules was determined to be 16.1 m² /g, and the averagepore diameter was 408 Å, as measured by mercury porosimetry. Thistechnique is a preferred method for measuring the size of pores greaterthan about 250 Å in diameter. The fired spherules were unchanged inappearance from the dried spherules. They were nearly all intact, butmany (>50%) were cracked.

A portion of the fired spherules was classified by size fraction asdescribed in Preparation A. Examination of the classified fractionsindicated that a portion of the spherules had fractured during theclassification procedure. Many intact spherules remained, but a portionof each fraction contained irregularly shaped particles which appearedto have been produced by the fracturing of the spherules during theclassification process.

Preparation C

To prevent the cracking observed in the spherules prepared according toPreparation B, spherules were also prepared as follows: 1250 g ofNyacol™ Zr 100/20 colloidal ZrO₂ were placed in a laboratory centrifugeand spun at 5000 rpm for 55 minutes. The supernatant was discarded andthe sediment was re-dispersed in distilled water. This centrifuged solwas placed on a rotary evaporator and concentrated until theconcentration of ZrO₂ in the sol was 32 wt %. To 513 g of this sol wereadded 34.6 g of a solution of zirconyl acetate containing 25% by weightZrO₂ equivalent (Harshaw, Inc., Cleveland, Ohio), and 61 g of a solutioncontaining 50 wt % PVP K30, a polyvinylpyrrolidone polymer (GAFCorporation, Texas City, Tex.) were added to the concentrated sol. Theresulting mixture was then agitated rapidly into a 50/50 mixture ofpeanut oil and oleyl alcohol which had been heated to a temperature of90° C. The resulting mixture contained gelled spherules of about 1 to30μ in diameter, which were observed under an optical microscope to beintact and crack-free.

The spherules were then fired to a temperature of 900° C. over 7 hoursand 20 minutes, with heating at a constant temperature of 900° C. for anadditional 6 hours. After firing, the resulting spherules were fromabout 1 to 25μ in diameter, and were observed under an opticalmicroscope to be intact and crack-free. The surface area and averagepore diameter of these microspheres were measured by mercury porosimetryto be 28 m² g and 415 Å, respectively. A portion of these spherules wasclassified into 5-10μ and 10-20μ fractions by sieving. Followingclassification, the classified spherules remained uncracked and intact.

EXAMPLE 9 Chemical Vapor Deposition of Carbon on Core ZrO₂ Spherules(Toluene as Carbon Source)

In order to deposit a thin film or cladding of carbon over the zirconiasubstrate, "bare" or unclad ZrO₂ spherules were treated as follows.

15 g of porous ZrO₂ spherules, prepared according to the procedure ofExample 8A above, which had a diameter of about 8μ and a surface area of56.5 m² /g and an average pore diameter of 90 Å, were placed in aceramic sample boat. The boat was placed in a reaction chamber within asmall tube furnace similar to that shown in FIG. 1. The vacuum pump ofthe system was engaged, and the total system pressure was lowered toabout 1 Torr (1 mm mercury). The furnace was then heated to atemperature of 700° C. After equilibrating at 700° C. for about 1 hour,the valve to the flask containing toluene at 22° C. was opened slightly,allowing toluene vapor to enter the reaction chamber. With this valveopen, the total pressure in the system rose to about 8 Torr, as measuredby the vacuum gauge. This gauge is calibrated to measure N₂ partialpressures. The effect of measuring the pressure of vapors such astoluene on the accuracy of the gauge is not known, but the gauge wasused as a means of measuring the relative pressures used in thepreparation of samples, instead of absolute pressures. The limits on thepressure of toluene are 0 Torr with the valve closed, to 23 Torr, whichis the vapor pressure of toluene at 22° C. The pressure was maintainedat a gauge reading of about 8 Torr for 10 minutes. During this time, theoriginally white ZrO₂ spherules turned black in color due to thedeposition of carbon on their surfaces.

After 10 minutes of deposition, the boat was removed from the furnacebut kept in the reaction chamber under vacuum by using a winch as shownin FIG. 1 to pull the sample from the furnace. After a cooling time ofabout 15 minutes, the spherules were removed from the reaction chamberand inspected. By visual observation, the spherules were free-flowingand undamaged by the low pressure CVD treatment. The specific surfacearea and average pore diameter of the spherules were measured and foundto be 38.7 m² /g and 113 Å, respectively.

EXAMPLE 10 Effect of Varying Deposition Time at 700° C.

This example describes an experiment designed to determine the effect ofdeposition time on amount of carbon deposited and spherule surface areaunder constant deposition conditions. Four tests were completed in whichsamples of ZrO₂ spherules underwent CVD of carbon for 5, 10, 20 and 25minutes, respectively. Each of the four samples consisted of 4 g ofporous ZrO₂ spherules, prepared according to the procedure of Example 8Aabove, having a particle size of about 1-10μ and a surface area of 48 m²/g. Each sample was placed in a sample boat similar to that shown inFIG. 1, which was then placed in the reaction chamber that had beenheated to 700° C. in the tubular furnace according to Example 9. Thesystem pressure was lowered to about 2 Torr by operation of the vacuumpump. After equilibrating for 10 minutes, the valve to the flaskcontaining toluene was opened slightly, thus allowing toluene vapor toenter the reaction chamber, until the total system pressure rose to avacuum gauge reading of about 5 Torr. This valve setting and temperaturewere maintained for the varying lengths of time shown in Table 10-1below. Each sample was then removed from the furnace, but kept withinthe reaction chamber under vacuum until the sample had cooled, about 15minutes. After cooling, the surface area and the weight percent carbonand hydrogen of each sample were measured, and are listed below in Table10-1.

                  TABLE 10-1                                                      ______________________________________                                        Deposition Time (min.)                                                                      Surf. Area (m.sup.2 /g)                                                                    Wt % C   Wt % H                                    ______________________________________                                         5            50           1.4      0.1                                       10            45           3.7      0.1                                       20            34           5.4      0.2                                       25            36           6.8      0.2                                       ______________________________________                                    

These results show that at a constant deposition temperature andpressure, the weight percent of the carbon coating increases, and thesurface area, in general, decreases with increasing deposition time.

EXAMPLE 11 Effect of Varying Deposition Time at 775° C.

This example describes the effect of varying the deposition time at 775°C., at a toluene vapor pressure of about 23 Torr as measured by a vacuumgauge, on the surface area of ZrO₂ spherules. 5 g of ZrO₂ spherulesprepared according to Example 2 and fired to 600° C., and having asurface area of 61 m² /g and an average pore diameter of 96 Å, wereplaced in a sample boat which was placed in the reaction chamber asdescribed in Example 10, with the exception that the temperature wasmaintained at 775° C. The pressure of the system was reduced to about 4Torr with the vacuum pump, and the system allowed to equilibrate forabout 10 minutes. When the valve leading to the flask which containedtoluene was opened, the total system pressure as measured by the vacuumgauge rose to about 27 Torr due to the presence of the toluene vapor. Oncontact with the heated sample, the toluene vapors decomposed, resultingin the deposition of a carbonaceous layer on the ZrO₂. Followingdecomposition for the times shown in Table 11-1 below, the samples wereremoved from the furnace but left in the reaction chamber under vacuumby winching from the furnace. After cooling in the quartz tube undervacuum for about 15 minutes, the surface area and average pore diameterof each sample was measured. Table 11-1 shows the results of theseexperiments.

                  TABLE 11-1                                                      ______________________________________                                        Deposition Time (min.)                                                                      Surf. Area (m.sup.2 /g)                                                                    Avg. Pore Dia. (Å)                             ______________________________________                                        2             38           112                                                5             38           102                                                10            31           101                                                ______________________________________                                    

The data in Table 11-1 show that the surface area and the average porediameter of the pores decreases with increasing deposition time.

EXAMPLE 12 Effect of Varying Deposition Temperature and Pressure

This example describes the deposition of the carbon layer at differentconditions of temperature and toluene partial pressure. Two samples,each comprising 8 g of porous ZrO₂ spherules prepared according toExample 8A above, were placed in a sample boat that was placed in thereaction chamber maintained at the deposition temperatures shown inTable 12-1 below. The system pressure was then lowered with the vacuumpump to about 2 Torr. After equilibrating the system for 10 minutes, thevalve to the toluene flask was opened, thus allowing toluene vapor toenter the reaction chamber. Deposition continued for the times shown inTable 12-1. After cooling under vacuum for about 15 minutes, the surfacearea, weight percent carbon, and weight percent hydrogen of each samplewere measured, and are listed in Table 12-1 below.

                  TABLE 12-1                                                      ______________________________________                                        Temp.                                                                         (°C.)                                                                          Time (min.)                                                                             Surf. Area (m.sup.2 /g)                                                                    Wt % C Wt % H                                  ______________________________________                                        1000     8         6.5         8.1    0.1                                      500    17        46.0         0.5    0.1                                     ______________________________________                                    

By visual observation, the 1000° C. sample was black in color, while the500° C. sample was tan in color. During deposition at 1000° C., a blackdeposit was also noted on the exit end of the reaction chamber. Thisexperiment showed that the rate of carbon deposition increases withincreasing deposition temperature.

EXAMPLE 13 Preparation of Carbon-Clad SiO₂ and Al₂ O₃ Spherules (Tolueneas Carbon Source)

This example describes treatment of porous SiO₂ and Al₂ O₃ spherules bythe low pressure CVD method to prepare carbon-clad SiO₂ and Al₂ O₃. Thebase silica spherules employed were HPLC Silica Nucleosil, fromMacherey-Nagel (Germany) which had a 15-25μ particle size. The basealumina spherules employed were SPHERISORB ALUMINA, obtained from PhaseSep Inc., Hauppauge, N.Y., which had about a 10μ particle size. For eachof three tests, a 0.9 g sample of spherules was placed in a sample boatand the boat was positioned in the quartz tubular reaction chamber atthe selected temperature shown in Table 13-1 below. The pressure in thereaction chamber was reduced to 5 Torr with a vacuum pump, and thesystem was allowed to equilibrate for 10 minutes. The valve to the flaskcontaining the toluene carbon source was then opened and the totalpressure raised to a vacuum gauge reading of about 9 Torr due to theintroduction of the toluene vapor. After deposition for the time periodsindicated in Table 13-1 below, each sample was allowed to cool undervacuum for about 15 minutes and its surface area, weight percent carbonand weight percent hydrogen were measured. The results are listed inTable 13-1, below.

                                      TABLE 13-1                                  __________________________________________________________________________    Sample                                                                             Temp. (°C.)                                                                   Time (min.)                                                                         Color                                                                             Surf. A (m.sup.2 /g)                                                                  Wt % C                                                                             Wt % H                                     __________________________________________________________________________    SiO.sub.2                                                                          700    10    white                                                                             103     0.4  <0.1                                       SiO.sub.2                                                                          800    10    black                                                                              80     2.0  <0.1                                       Al.sub.2 O.sub.3                                                                   700    10    black                                                                             113     4.2   0.6                                       __________________________________________________________________________

The results indicate that the present low pressure CVD method is usefulfor carbon cladding other inorganic oxides besides ZrO₂. However, thedata of Table 13-1 indicate that a higher temperature (i.e., greaterthan 700° C.) may be required to effect equivalent levels of carbondeposition from toluene onto SiO₂, than the temperature required toeffect carbon deposition onto Al₂ O₃ or ZrO₂ (less than or up to about700° C.).

EXAMPLE 14 Reductive Treatment of ZrO₂ Carbon-clad Spherules

This example describes heat treatment of carbon-clad ZrO₂ spherulesprepared according to Example 9 while exposing them to a reducingatmosphere. The purpose of the heat treatment was to cause the reductionof polar functional groups on the carbon-clad surface of the spherules,thereby modifying chromatographic performance by increasing thehomogeneity of the surface of the spherules.

A 20 g sample of carbon-clad ZrO₂ spherules prepared according toExample 9 (toluene hydrocarbon source) was placed in an Al₂ O₃ sampleboat inside of a mullite tubular reaction chamber with gas tight sealson both ends. The reaction chamber was then placed within a tubularfurnace, in accordance with the arrangement depicted in FIG. 1. Thesample of ZrO₂ spherules was exposed to a gaseous reducing mixture of95% Ar/5% H₂ by flowing this mixture through the reaction chamber. Afterallowing the system to equilibrate for about 30 minutes, the sample washeated to a temperature of 700° C. over 2 hours, and thereaftermaintained at 700° C. for an additional hour. At the end of the thirdhour, the furnace was shut off and the samples allowed to cool in thetube, still under the flow of 95% Ar/5% H₂.

EXAMPLE 15 Use of n-Heptane as Carbon Source

This example describes the use of n-heptane, rather than toluene, as thecarbon source for the present low pressure CVD process. A 9 g sample ofZrO₂ spherules prepared according to Example 8A, which had a diameter ofabout 5μ, a surface area of 40 m² /g, and an average pore diameter ofabout 164 Å, were placed in a sample boat similar to that shown inFIG. 1. The boat was positioned in the quartz tubular reaction chamberas in the previous examples. The system was equilibrated at atemperature of 700° C. and a pressure of about 1 Torr for 10 minutes.The valve to the flask containing n-heptane was then opened slightly,bringing the total system pressure to about 5 Torr as measured by thevacuum gauge, due to the presence of n-heptane vapor. These conditionswere maintained for 20 minutes before the sample was winched from thefurnace and allowed to cool under vacuum for about 15 minutes. By visualobservation, the clad spherules ranged from dark grey to black in color.It was also observed that the portion of the sample located nearer tothe top of the sample boat was darker in color than the portion of thesample below.

EXAMPLE 16 Effect of Repeated Carbon-cladding

This example describes experiments in which a thin cladding of carbonwas deposited on a sample of ZrO₂ spherules as described in the previousexamples, the carbon-clad sample was mixed or stirred up, and additionalcarbon was then deposited by repeating the CVD in order to improvecoating homogeneity.

A sample of ZrO₂ spherules prepared according to Example 8A, which had adiameter of about 5μ, a surface area of 4Q m² /g, and an average porediameter of 164 Å, were heated to a temperature of 700° C., and held atthis temperature for 6 hours prior to the cladding procedure. Two testswere performed, one employing toluene as the carbon source, the otherusing n-heptane. The amount of carbon source vaporized during each testwas determined by weighing each flask at the beginning and the end ofeach test. The temperature maintained in the furnace during each testwas 700° C., and in both tests the original system pressure was about 6Torr. Each sample underwent carbon vapor deposition for 15 minutes,cooling for 15 minutes, thorough mixing of the sample, and a secondcarbon vapor deposition for another 15 minutes. After cooling for about15 minutes following the second carbon deposition, the surface area,weight percent carbon, and weight percent hydrogen of each sample wereanalyzed, and are listed in Table 16-1 below.

                                      TABLE 16-1                                  __________________________________________________________________________    CARBON                                                                              WEIGHT   SURFACE WEIGHT %                                                                             WEIGHT %                                        SOURCE                                                                              VOLATILIZED                                                                            AREA (m.sup.2 /g)                                                                     C      H                                               __________________________________________________________________________    n-Heptane                                                                            6.5 g   24      1.1    <0.1                                            Toluene                                                                             12.5 g   25      3.1    <0.1                                            __________________________________________________________________________

EXAMPLE 17 Determination of Exposed Zirconia

A technique was developed to determine the amount of bare ZrO₂ remainingexposed, i.e., not clad with carbon, after carrying out the CVD processof the present invention on ZrO₂ spherules. The technique is based onthe known strong adsorption of phosphate ions on ZrO₂ surfaces. Morespecifically, the amount of remaining exposed zirconia was determined bymonitoring phosphate removal from a solution in contact with thecarbon-clad zirconia spherules as follows:

In a static adsorption study, a 0.1 g sample of carbon-clad spheruleswhich had been prepared according to Example 9 above was placed in aclean 30 ml polyethylene bottle. A 2 mM to 10 mM standard solution ofphosphate was prepared from phosphoric acid and water having aresistivity of greater than 16 megaohms. Twenty ml of the phosphatesolution were added to the polyethylene bottle, and a vacuum was appliedwith sonication to completely wet the pores of the spherules. Themixture of spherules in phosphate solution was then agitated every 30min for the next 6 to 8 hours. Following agitation, the mixture wasallowed to stand for 20-24 hours. At the end of the standing period, thephosphate solution was removed from the polyethylene bottle with a 10 mlglass syringe and passed through a 0.2 um filter to remove any remainingzirconia particles.

The filtered solutions and blanks (standard phosphate solutions) wereanalyzed for phosphorous using Inductively Coupled Plasma Spectroscopy(ICPS). The amount of phosphorous that had adsorbed to the spherules wasdetermined by the difference between phosphate concentration in thestandard solutions (blanks) and the filtered solutions. The ICPSanalysis indicated that 90-95% of the surface area of the ZrO₂ substratehad been blocked from interaction with the phosphate solute by thecarbon coating.

An additional technique used to determine the carbon coverage of theZrO₂ spherules involved observation of the breakthrough of a UV-activeorganophosphate compound such as phenylphosphate through achromatographic column.

EXAMPLE 18 Analysis of Carbon-clad ZrO₂ Spherules

A. Column Packing

A 5×0.46 cm HPLC column was packed with the carbon-clad ZrO₂ spherulesof Example 9 (toluene carbon source) using an upward slurry technique.This technique involved the use of (i) a first slurry solvent such ashexane or tetrahydrofuran (THF) to suspend the packing material; and(ii) a relatively viscous, miscible solvent such as isopropanol ormethanol to displace the slurry into the column. In this manner, thecolumn could be tightly packed at a relatively low flow rate, e.g., upto about 5 ml/min, once the column bed had been established. The columnwas packed at a pressure of about 6000-9000 psi. Utilization of thelower flow rate (5 ml/min) at these pressures advantageously avoided anysignificant amount of solvent consumption.

B. Chromatographic Nature

In order to test the chromatographic nature of the carbon-clad supportmaterial of the present invention, a chromatographic study was performedusing a 5×0.46 cm HPLC column packed with the carbon-clad ZrO₂ spherulesof Example 9 (toluene carbon source) as the stationary phase. A 70/30 (%v/% v) tetrahydrofuran/water solution at 35° C. was used as the mobilephase.

A 5 μl sample of a mixture of alkylbenzenes was injected onto the packedHPLC column. The resulting chromatogram is shown in FIG. 2a. Aftercompletion of the separation of the alkylbenzenes, a 5 μl sample of amixture of alkylphenones was also separated on the column, underidentical conditions. The resulting chromatogram is shown in FIG. 2b.Capacity factors (i.e., the ratio of solute concentration in thestationary phase to solute concentration in the mobile phase) werecalculated for each solute by evaluating the ratio (t_(r) -t_(o))/t_(o),where t_(r) is retention time measured at peak maximum, and t_(o) iscolumn dead time measured by solvent mismatch.

FIG. 3 depicts a plot of logarithm of the capacity factor k' vs. carbonnumber of the components of the alkylbenzene mixture (ethylbenzenethrough hexylbenzene) and for the components of the alkylphenone mixture(acetophenone through hexanophenone). As depicted in FIG. 3, the pointsfor the homologous series fall on a straight line; the alkylphenones aremore retained that the alkylbenzenes; and the slope of the log k' vs.carbon number line for the alkylphenones is slightly greater than thatfor the alkylbenzenes. These results indicate that the carbon-cladspherules employed as the stationary phase act as a reversed phasematerial. More specifically, the reversed phase character of thespherules is demonstrated by (i) the linear relationship betweenlogarithm of the capacity factor, k', and the number of methylene groupsfor a homologous series of solutes; and (ii) the decreasing retention ofthose solutes as the mobile phase organic modifier concentration wasincreased.

The greater retention of the alkylphenones than the alkylbenzenesindicates the strong interaction of the present carbon-clad ZrO₂ withpolarizable compounds, especially aromatic polarizable compounds. Thegreater retention of the alkylphenones than the alkylbenzenes is theconverse of what is observed with bonded phase reversed phase liquidchromatography (RPLC) supports. However, greater retention ofalkylphenones than alkylbenzenes is observed on carbon-based supportssuch as graphitized and pyrolytic carbon.

C. Alkaline Stability

The alkaline stability of carbon-clad ZrO₂ spherules prepared accordingto Example 9 was tested by repeatedly injecting varying amounts of atest solute, benzene, into a 12.5×0.46 cm HPLC column packed with thespherules. A continuous flow of hot alkaline mobile phase of 50%methanol/50% pH 12 water was maintained through the column at atemperature of 80° C. and a flow rate of 0.5 ml/min. During the 60 hourstudy, a total of 2 liters of the alkaline mobile phase passed throughthe column. As shown in FIG. 4, the retention of benzene was quiteconstant under these conditions.

After completion of the chromatographic stability tests, the packing wasremoved from the column and analyzed for carbon, hydrogen, and nitrogencontent. The results of the CHN analysis, depicted in Table 18-1 below,indicate that essentially none of the carbon was lost from the surfaceof the packing during the alkaline stability study. Thus, the CHNresults confirm the results of the chromatographic stability tests.

                  TABLE 18-1                                                      ______________________________________                                        CHN Analysis Results.sup.2                                                    Source       % C          % H    % N                                          ______________________________________                                        Column Front 3.3          0.2    <0.1                                         Column End   3.4          0.2    <0.1                                         Column Middle                                                                              3.3          0.2    <0.1                                         Fresh.sup.1  3.4          0.2    <0.1                                         ______________________________________                                         .sup.1 Fresh = not exposed to alkaline conditions.                            .sup.2 Precision of this analysis was ± 0.1%.                         

EXAMPLE 19 Exposure of CVD Carbon-Clad ZrO₂ Particles to ReducingConditions

A. Reduction of Polar Surface Groups

An experiment was performed to examine the effect on chromatographicperformance of the carbon-clad (toluene carbon source) ZrO₂ spheruleswhen the spherules were exposed to reducing conditions. A 30 g sample ofcarbon-clad ZrO₂ spherules was prepared, and immediately thereafterexposed to a 95% argon/5% hydrogen atmosphere at a temperature of 700°C. for 60 minutes, as described in Example 14. These conditions wereexpected to reduce the number of polar oxygenated sites which may bepresent on the carbon surface.

B. Chromatographic Nature of Reduced Material

The reduced material was then packed into a 15 cm×0.46 cm HPLC columnwith which several chromatographic studies were carried out. Packing wasperformed by means of the upward slurry technique described in Example18. Separations were performed of a mixture of alkylphenones and amixture of alkylbenzenes, using the reduced, carbon-clad zirconia as thestationary phase and a mobile phase of 70% THF/30% water. FIG. 5 depictsa plot of log(capacity factor) vs. carbon number for each alkylphenonecomponent and alkylbenzene component of the mixture.

FIG. 5 indicates that the reduced, carbon-clad stationary phase wasoperating in reversed-phase mode, since the points for both homologousseries fall on a straight line, and the capacity factors increase uponlowering the concentration of organic modifier in the mobile phase.Comparison of FIG. 5 with FIG. 3 indicates that reductive treatment ofthe carbon-clad ZrO₂ had little effect on capacity of the material toretain alkylbenzenes, but had a significant effect on the capacity ofthe material to retain alkylphenones. The slope of the log(capacityfactor) vs. carbon number line for alklyphenones is less in FIG. 5 thanin FIG. 3, and more closely approximates the slope of the log(capacityfactor) vs. carbon number line for alkylbenzenes. These trends indicatethat some of the exceptionally strong adsorption sites on the carbonsurface were quenched by the reductive treatment.

In an additional experiment, the efficiency of the HPLC column, packedwith the reduced carbon-clad ZrO₂ prepared as described in part A, wascompared to the efficiency of a column packed with unreduced carbon-cladZrO₂, prepared as described in Example 9. Butyrophenone was injected ata reduced velocity of 20, and a 60% THF/40% water mobile phase wasmaintained at 35° C. in both columns. The results indicated thatchromatographic efficiency increased by 200% when the reduced supportmaterial was used as the stationary phase instead of the non-reducedsupport material.

In conclusion, these studies showed that the carbon-clad ZrO₂ spherulesare a useful reversed phase support and show strong retention ofnonpolar solutes and superior alkaline stability and solute selectivity.Furthermore, exposure of the carbon-clad coated ZrO₂ spherules toreducing conditions prior to their utilization in separations improvesthe efficiency of those separations.

EXAMPLE 20 Preparation of Carbon-Clad ZrO₂ - and Silica-Packed HPLCColumns

Carbon-clad ZrO₂ spherules prepared according to Example 9 above, butwith a 15 minute deposition time, were evaluated as a chromatographicsupport material. The spherules had a ca 5 μm particle diameter, 100 Åmean pore diameter, and a specific surface are of ca 50 m² /g.

The carbon-clad ZrO₂ support was packed into a 10×0.21 cm equipped withKel-F encased 2 mm o.d. SS frits by the upward slurry packing techniquedescribed in Example 18. Two grams of the support material were slurriedand outgassed under vacuum in 17.5 ml of a 5:1 (v/v) hexane/1-octanolsolution. The resulting slurry was used to pack the column at 6000 psiusing practical grade hexane as solvent. The packed column wassubsequently washed with 2-propanol (IPA) and acetonitrile (ACN), andwas equilibrated with water/acetonitrile (HOH/ACN) mobile phase forcharacterization in reversed-phase chromatography.

A 10×0.2 cm commercial Hypersil (silica) ODS (C18) column was obtainedfrom the Hewlett-Packard Company, Avondale, Pa.

EXAMPLE 21 Comparison of Solute Retention with Varying Organic MobilePhase Modifier Concentration on Carbon-Clad ZrO₂ - and and Silica-PackedColumns

In order to evaluate the nature of solute retention on the carbon-cladZrO₂ stationary phase of Example 20, the isocratic elution of a mixtureof alkyl benzene solutes was analyzed while employing HOH/ACN mobilephases of varying ACN concentration. The sample mixture of alkylbenzenes included benzene, toluene, ethyl benzene, n-propyl benzene, andn-butyl benzene (0.8 mg/ml each in 3/2 methanol/water). One microliterinjections of the sample were performed into mobile phase compositionsof 65/35, 60/40, 55/45, 50/50, 45/55, 40/60, 35/65, and 30/70 v/vHOH/ACN at a flow rate of 0.500 ml/min while the column was thermostatedat 40° C. Chromatographic characterization was performed on aHewlett-Packard model 1090M HPLC system equipped with a 0.6 cmpathlength diode array absorbance detector. The elution of the soluteswas detected by absorbance at 215 nm. The peak maximum in the absorbancetrace was taken as the retention time for each solute in each mobilephase.

For comparison, the same set of injections were made under identicalconditions using the commercial Hypersil ODS (C18) column described inExample 20.

A comparison of the actual retention time data for the alkyl benzenes onthe carbon-clad ZrO₂ -packed column with that of the solutes on thetraditional silica-based commercial Hypersil ODS (C18) column is shownin Table 21-1 below:

                                      TABLE 21-1                                  __________________________________________________________________________    RETENTION OF ALKYL BENZENES AS A FUNCTION OF                                  % ORGANIC:                                                                    solute    ZrO.sub.2                                                                         SiO.sub.2                                                                        ZrO.sub.2                                                                         SiO.sub.2                                                                        ZrO.sub.2                                                                         SiO.sub.2                                                                        ZrO.sub.2                                                                         SiO.sub.2                                  __________________________________________________________________________              65/35 W/A                                                                            60/40 W/A                                                                            55/45 W/A                                                                            50/50 W/A                                      BENZENE   1.84                                                                              2.65                                                                             1.45   1.17                                                                              1.60                                                                             0.990                                                                             1.32                                       TOLUENE   3.69                                                                              4.79                                                                             2.56   1.91                                                                              2.42                                                                             1.493                                                                             1.85                                       ETHYL BENZENE                                                                           5.75   3.69   2.57                                                                              3.71                                                                             1.893                                                                             2.66                                       PROPYL BENZENE                                                                          13.80  7.82   4.96                                                                              6.14                                                                             3.370                                                                             4.12                                       BUTYL BENZENE                                                                           >20    17.50  10.26                                                                             10.28                                                                            6.443                                                                             6.48                                                 45/55 W/A                                                                            40/60 W/A                                                                            35/65 W/A                                                                            30/70 W/A                                      BENZENE   0.87                                                                              1.11                                                                             0.78                                                                              0.95                                                                             0.71                                                                              0.84                                                                             0.657                                                                             0.758                                      TOLUENE   1.21                                                                              1.48                                                                             1.03                                                                              1.21                                                                             0.89                                                                              1.03                                                                             0.799                                                                             0.897                                      ETHYL BENZENE                                                                           1.47                                                                              2.00                                                                             1.19                                                                              1.56                                                                             1.01                                                                              1.28                                                                             0.871                                                                             1.071                                      PROPYL BENZENE                                                                          2.41                                                                              2.91                                                                             1.83                                                                              2.16                                                                             1.44                                                                              1.69                                                                             1.192                                                                             1.356                                      BUTYL BENZENE                                                                           4.31                                                                              4.34                                                                             3.06                                                                              3.06                                                                             2.27                                                                              2.28                                                                             1.762                                                                             1.742                                      __________________________________________________________________________     "W" = water                                                                   "A"  = acetonitrile                                                      

The results shown in Table 21-1 indicate that the retention of n-butylbenzene is virtually identical on both columns. For the remaining alkylbenzene solutes (ethyl through butyl), the retentions on the two phasesare roughly comparable.

EXAMPLE 22 Comparison of Capacity Factor for Separations withCarbon-Clad ZrO₂ -Packed HPLC Column and Silica-Packed Column

The retention characteristics of several substituted benzene soluteswere compared during isocratic reversed-phase chromatography on thecarbon-clad ZrO₂ -packed column and the commercial Hypersil ODS columnof Example 20. 0.2 μl injections of the alkyl benzene solute solutioninto a 2/1 water/ACN (1/1 water/ACN for iodobenzene) mobile phase weremade for each of the columns, and equilibrated with 65/35 v/v water/ACNat 0.500 ml/min and 40° C. The concentration of solute in the sampleswas 1-4 ppt (mg/ml or μl/ml). Absorbance was detected at both 215 nm and260 nm. The dead volume characteristics of both of the columns wereprobed by injectioning solutions of deuterium oxide (D₂ O)/ACN anddilute solutions of uracil and of sodium nitrate.

The capacity factors (k') for the various solutes were calculated fromthe retention times (tR) after correction for the experimentallydetermined extracolumn dead volume of 35 μl, based on approximate deadvolumes of 200 μl and 150 μl for the carbon-clad ZrO₂ column and theHypersil column, respectively. The capacity factors are listed in Table22-1 below:

                                      TABLE 22-1                                  __________________________________________________________________________    COMPARISON OF CARBON CLAD ZIRCONIA WITH COMMERCIAL C18 SILICA                                           5 mm CARBON-    HYPERSIL 5 mM                                        mg/ml    CLAD ZrO.sub.2  C18 SiO.sub.2                       Solute           mg/ml                                                                             Solvent                                                                            tR      k'      tR k'                               __________________________________________________________________________                              0.40            0.30                                D.sub.2 O                 0.55    0.19    0.37                                                                             -0.01                            ACETONITRILE (CH.sub.3 CN)                                                                              0.54    0.17    0.46                                                                             0.30                             URACIL (C.sub.4 H.sub.4 N.sub.2 O.sub.2)                                                       1.2 H.sub.2 O                                                                          0.98    1.29    0.39                                                                             0.08                             PHENOL (C.sub.6 H.sub.5 OH)                                                                    4.4 2/1 W/A                                                                            1.33    2.15    0.92                                                                             1.82                             ANILINE (C.sub.6 H.sub.5 NH.sub.2)                                                             3.3 2/1 W/A                                                                            1.45    2.45    1.32                                                                             3.17                             BENZENE (C.sub.6 H.sub.6)                                                                      3.3 2/1 W/A                                                                            1.83    3.39    2.65                                                                             7.61                             m - CRESOL (C.sub.6 H.sub.4 CH.sub.3 OH)                                                       3.3 2/1 W/A                                                                            2.19    4.30    1.22                                                                             2.82                             p - CRESOL (C.sub.6 H.sub.4 CH.sub.3 OH)                                                       3.3 2/1 W/A                                                                            2.23    4.39    1.18                                                                             2.70                             FLUORO BENZENE (C.sub.6 H.sub.5 F)                                                             3.3 2/1 W/A                                                                            2.25    4.45    2.88                                                                             8.35                             o - CRESOL (C.sub.6 H.sub. 4 CH.sub.3 OH)                                                      3.3 2/1 W/A                                                                            2.51    5.11    1.32                                                                             3.18                             BENZONITRILE (C.sub.6 H.sub.5 CN)                                                              3.3 2/1 W/A                                                                            3.07    6.51    1.57                                                                             4.00                             BENZALDEHYDE (C.sub.6 h.sub.5 CHO)                                                             3.3 2/1 W/A                                                                            3.60    7.82    1.31                                                                             3.13                             TOLUENE (C.sub.6 H.sub.5 CH.sub.3)                                                             3.3 2/1 W/A                                                                            3.61    7.85    4.79                                                                             14.72                            CHLORO BENZENE (C.sub.6 H.sub.5 Cl)                                                            3.3 2/1 W/A                                                                            5.42    12.37   4.88                                                                             15.03                            m - XYLENE (C.sub.8 H.sub.10)                                                                  3.3 2/1 W/A                                                                            7.02    16.38   8.51                                                                             27.14                            p - XYLENE (C.sub.8 H.sub.10)                                                                  3.3 2/1 W/A                                                                            7.99    18.80   8.60                                                                             27.44                            BROMO BENZENE (C.sub.6 H.sub.5 Br)                                                             3.3 2/1 W/A                                                                            7.19    16.81                                       NITRO BENZENE (C.sub.6 H.sub.5 NO.sub.2)                                                       3.3 2/1 W/A                                                                            7.78    18.29   2.08                                                                             5.71                             o - XYLENE (C.sub.8 H.sub.10)                                                                  3.3 2/1 W/A                                                                            9.73    23.16   7.89                                                                             25.06                            IODO BENZENE (C.sub.6 H.sub.5 I)                                                               3.3 1/1 W/A                                                                            14.57   35.24   7.65                                                                             24.27                            BENZOIC ACID (C.sub.6 H.sub.5 COOH)                                                            3.4 2/1 W/A                                                                            >>20    >>65    0.54                                                                             0.57                             Na BENZENE SULFONATE                                                                           3.4 2/1 W/A                                                                            >>20    >>65    0.33                                                                             -0.12                            (C.sub.6 H.sub.5 NaO.sub.3 S)                                                 __________________________________________________________________________

The results shown in Table 22-1 indicate several unique features of thecarbon-clad ZrO₂ material. Oxygen-containing solutes (e.g., uracil,phenol, cresols, benzaldehyde, and acids) were significantly moreretained on the carbon-clad ZrO₂ material than on the Hypersil (silica)support material. In addition, solutes having strongly dipolar andpolarizable groups (e.g., uracil, benzonitrile, benzaldehyde,nitrobenzene, and iodobenzene) were significantly more retained on thecarbon-clad ZrO₂ support than on the Hypersil (silica) support. The purehydrocarbon solutes (e.g., benzene, toluene, xylene) were more stronglyretained on the Hypersil (silica) support material than on thecarbon-clad ZrO₂ material. The retention of polysubstituted species suchas the xylenes and the cresols indicates a geometric dependency on thecarbon-clad ZrO₂ material with a retention order of meta<para<ortho. Incontrast, the Hypersil (silica) material exhibited differing retentionorders of para<meta<ortho< and ortho<meta <para for the cresols and thexylenes, respectively.

EXAMPLE 23 Comparison of Capacity Factor for Carbon-Clad ZrO₂ -PackedHPLC Column and Silica-Packed Column under Acidic and Basic Conditions

The retention on the 10 cm×2.1 mm carbon-clad ZrO₂ -packed column ofExample 20 was also evaluated under acidic (1% formic acid, HCOOH) andbasic (0.10M sodium hydroxide, NaOH) aqueous solvent conditions. 0.2 μlsamples were injected onto the carbon-clad ZrO₂ column, equilibratedwith 65/35 aqueous./ACN solvent, were eluted isocratically, and weredetected as described above. The results are shown in Table 23-1 below,which lists the retention times of various test solutes for 0.5 ml/min.,40° C. mobile phases of 65/35 1% formic acid (HCOOH)/ACN, for 65/35water/ACN, and for 0.1M (pH 13) sodium hydroxide (NaOH)/ACN:

                                      TABLE 23-1                                  __________________________________________________________________________    COMPARISON OF RETENTION ON CARBON CLAD ZIRCONIA: pH EFFECTS                                               5 mm CARBON COATED                                                            ZIRCONIA COLUMN:                                                                            35/65 ACN/                                                      35/65 ACN/                                                                           35/65  0.1M (pH 13)                                                    1% HCOOH                                                                             ACN/H.sub.2 O                                                                        NaOH                                Solute         mg/ml                                                                             Solvent  tR     tR     tR                                  __________________________________________________________________________    SODIUM NITRATE     H.sub.2 O       0.72   0.37                                D20                --       0.58   0.54   0.44                                ACETONITRILE       --       0.58   0.53   0.42                                URACIL         1.2 H.sub.2 O                                                                              0.65   0.98   0.38                                PHENOL         4.4 2/1 W/A  1.22   1.32   0.41                                ANILINE        3.3 2/1 W/A  0.53   1.44   0.92                                BENZENE        3.3 2/1 W/A  1.55   1.82   1.28                                m - CRESOL     3.3 2/1 W/A  1.86   2.19   0.46                                p - CRESOL     3.3 2/1 W/A  1.93   2.22   0.49                                FLUORO BENZENE 3.3 2/1 W/A  1.90   2.25   1.57                                o - CRESOL     3.3 2/1 W/A  2.16   2.51   0.52                                BENZONITRILE   3.3 2/1 W/A  2.76   3.07   2.29                                BENZALDEHYDE   3.3 2/1 W/A  3.04   3.59   2.87                                TOLUENE        3.3 2/1 W/A  3.17   3.60   2.48                                CHLORO BENZENE 3.3 2/1 W/A  4.81   5.41   3.75                                ETHYL BENZENE  4   2/1 W/A  4.43   5.75   3.72                                m - XYLENE     3.3 2/1/2                                                                             W/A/M                                                                              5.69   7.02   4.62                                p - XYLENE     3.3 2/1 W/A  6.33   7.99   5.24                                BROMO BENZENE  3.3 2/1 W/A  6.35   7.19   5.19                                NITRO BENZENE  3.3 2/1 W/A  6.70   7.78   5.84                                o - XYLENE         2/1 W/A  7.61   9.73   6.49                                n-PROPYL BENZENE                                                                             4.0 2/1/2                                                                             W/A/M                                                                              10.10  13.80  8.30                                IODO BENZENE   3.3 2/1 W/A  12.35  14.56  9.75                                BENZOIC ACID   3.4 2/1 W/A  8.15   >>20   0.37                                Na BENZENE SULFONATE                                                                         3.4 2/1 W/A  >>20   >>20   0.37                                __________________________________________________________________________

The usefulness of the carbon-clad ZrO₂ stationary phase for separationsin which either strongly acidic or basic mobile phases are utilized isdemonstrated by the retention data in Table 23-1. The results indicatethat the retention of solutes with ionizable acidic and basic groupschange dramatically with changes in pH of the mobile phase, while theshifts in retention for other solutes are significantly less for theextreme pH mobile phases. Most significantly, solutes such as benzoicacid and benzene sulfonate, which are strongly retained in acidic andneutral solutions, elute in the dead volume of the hydroxide solution.Conversely, aniline retention drops dramatically in acidic solutionrelative to neutral or basic mobile phases.

These trends are even more apparent when represented as selectivityvalues (α) relative to benzene, as shown in Table 23-2 below:

                                      TABLE 23-2                                  __________________________________________________________________________    ALPHA VALUES (RELATIVE TO BENZENE) FOR CARBON CLAD ZIRCONIA                   k'(x)/k'(benzene)                                                                                         5 mm CARBON COATED                                                            ZIRCONIA COLUMN:                                                              35/65 ACN/                                                                           35/65  35/65 ACN/                                                      1% HCOOH                                                                             ACN/H.sub.2 O                                                                        0.1M NaOH                           Solute         mg/ml                                                                             Solvent  tR     tR     tR                                  __________________________________________________________________________    URACIL         1.2 H.sub.2 O                                                                              0.39   0.52   0.26                                PHENOL         4.4 2/1 W/A  0.77   0.71   0.28                                ANILINE        3.3 2/1 w/A  0.31   0.78   0.70                                BENZENE        3.3 2/1 W/A  1.00   1.00   1.00                                m - CRESOL     3.3 2/1 W/A  1.21   1.20   0.32                                p - CRESOL     3.3 2/1 W/A  1.25   1.22   0.35                                FLUORO BENZENE 3.3 2/1 W/A  1.23   1.24   1.24                                o - CRESOL     3.3 2/1 W/A  1.41   1.39   0.37                                BENZONITRILE   3.3 2/1 W/A  1.81   1.71   1.83                                BENZALDEHYDE   3.3 2/1 W/A  2.00   2.00   2.31                                TOLUENE        3.3 2/1 W/A  2.09   2.01   1.99                                CHLORO BENZENE 3.3 2/1 W/A  3.20   3.04   3.03                                ETHYL BENZENE  4   2/1/2                                                                             W/A/M                                                                              2.94   3.23   3.01                                m - XYLENE     3.3 2/1 W/A  3.79   3.96   3.75                                p - XYLENE     3.3 2/1 W/A  4.22   4.51   4.26                                BROMO BENZENE  3.3 2/1 W/A  4.23   4.05   4.22                                NITRO BENZENE  3.3 2/1 W/A  4.47   4.39   4.76                                o - XYLENE         2/1 W/A/M                                                                              5.09   5.50   5.29                                n-PROPYL BENZENE                                                                             4.0 2/1/2                                                                             W/A/M                                                                              6.76   7.82   6.79                                IODO BENZENE   3.3 2/1 W/A  8.28   8.25   7.98                                BENZOIC ACID   3.4 2/1 W/A  5.45   --     0.25                                Na BENZENE SULFONATE                                                                         3.4 2/1 W/A  --     --     0.25                                *assuming VO = 200 ml       3.70   4.383.03                                   __________________________________________________________________________

EXAMPLE 24 Comparison of Toluene and Heptane as Carbon Sources

The following experiments were performed in order to study the effect ofvarying the carbon source used in the present low pressure CVD method onchromatographic performance of the resulting spherules.

Two approximately 5 g batches of carbon-clad ZrO₂ spherules wereprepared, one according to the procedure of Example 9 (toluene carbonsource), and the other according to the procedure of Example 15(n-heptane carbon source). Samples from each batch were used as thepacking of two 5×0.46 cm HPLC columns operated with a 40° C. mobilephase of 40% THF and 60% water. The upward slurry packing techniquedescribed in Example 18 was used to pack both columns. An identicalmixture of ethylbenzene (EtBen) and nitrobenzene (NitroBen) wasseparated on each column. The results of the separations are shown inTable 24-1 below:

                  TABLE 24-1                                                      ______________________________________                                        Comparison of CVD Heptane and                                                 CVD Toluene Chromatographic Efficiency                                        Flow Rate.sup.1                                                                         CVD Heptane     CVD Toluene                                         (ml/min)  h.sup.2 -EtBen                                                                          h-NitroBen                                                                              h-EtBen                                                                              h-NitroBen                               ______________________________________                                        1.5       4.5       5.8       14.8   342                                      1.0       4.3       5.3       13.5   236                                      0.5       3.6       4.7       15.0   --                                       0.35      3.6       4.8       14.2   283                                      0.2       5.6       5.0       19.3   239                                      ______________________________________                                         .sup.1 flow rate of mobile phase                                              .sup.2 h = reduced plate height                                          

The high values of reduced plate height, indicating poor chromatographicefficiency, and the weak dependence on flow rate observed in Table 24-1for the column prepared using toluene as the carbon source, indicatethat the reduced chromatographic efficiency is due to chemicalprocesses, instead of sluggish diffusion in micropores or similarphysical processes.

Additional separations of a mixture of ethylbenzene, butylphenyl ether,propiophenone, and nitrobenzene were performed on both columns. Capacityfactors (k') and reduced plate heights (h) were calculated for eachsolute, and are shown in Table 24-2 below:

                  TABLE 24-2                                                      ______________________________________                                        Chromatographic Separation of Different Solutes                               on CVD Heptane and CVD Toluene                                                               CVD Heptane                                                                             CVD Toluene                                          Solute           k'      h       k'    h                                      ______________________________________                                        Ethylbenzene     3.3     4.5     2.4    11                                    Butylphenyl Ether                                                                              10.0    7.4     5.1    28                                    Propiophenone    3.8     7.6     2.5   120                                    Nitrobenzene     3.6     5.3     5.5   194                                    ______________________________________                                    

Loading studies of both columns were also performed by calculating thecapacity factor, k', for various amounts of sample which were injectedonto the columns. A mobile phase of 40% THF/60% water was maintainedthroughout the study at a temperature of 40° C. and a flow rate of 1ml/min. The sample was an aqueous solution of nitrobenzene, at aconcentration of approximately 10 mg nitrobenze/ml solution. The resultsof the loading studies are shown in Table 24-3 below:

                  TABLE 24-3                                                      ______________________________________                                        Comparison of Chromatographic                                                 Loading on CVD n-Heptane and CVD Toluene                                      Amt Injected                                                                              CVD n-Heptane CVD Toluene                                         (mg)        k'     % change   k'   % change                                   ______________________________________                                        0.01        3.75              13.3                                                               1.3             27                                         0.02        3.70              9.7                                                                1.3             36                                         0.05        3.65              6.2                                                                1.4             31                                         0.10        3.60              4.3                                             ______________________________________                                    

The results shown in Tables 24-1, 24-2, and 24-3 indicate that thesupport material prepared by deposition of carbon from thermaldecomposition of n-heptane exhibits significantly improvedchromatographic efficiency and loading characteristics as compared tothe support material prepared from thermal decomposition of toluene.These results also indicate that variation in the carbon source canstrongly affect the various chromatographic properties (e.g., retention,capacity, selectivity and efficiency) of the resultant materials. Thus,control and variation of the carbon source material, together withoptional reductive treatment as described in Example 14, can providediffering reversed phase materials suitable for differing separationneeds.

EXAMPLE 25 Use of n-Butanol as Carbon Source

A. Preparation of Carbon-Clad ZrO₂

A 6.04 g sample of ZrO₂ spherules prepared according to Example 8A wasplaced in a ceramic sample boat which was then centerally located in adeposition chamber maintained at 700° C. With initial system pressureestablished at 0.95 Torr, n-butanol was released into the chamber untilthe system pressure as measured by the vacuum gauge had increased to 6Torr. Pressure was maintained at between 5.5-6.4 Torr throughout thedeposition process. After 45 minutes of carbon deposition, the samplewas removed from the deposition chamber and allowed to cool under vacuumfor 25 minutes. By visual observation, the particles located at the topof the sample boat were very dark in color, but those at the bottom ofthe sample boat were much lighter, indicating a less complete carboncladding of these particles. The deposition process was repeated asecond time after thorough mixing of the particle bed. During the seconddeposition process, the system pressure was maintained at a vacuum gaugereading of between 6.5-12 Torr by warming the carbon source flaskcontaining the n-butanol. After 20 minutes of carbon deposition, thesample was removed and allowed to cool under vacuum for 25 minutes.

B. Chromatographic Analysis

The carbon-clad spherules prepared as described in part A above werepacked into a 5×0.46 cm HPLC column using the upward slurry techniquedescribed in Example 18 above. A 50% THF/50% water mobile phasemaintained at a temperature of 40° C. and a flow rate of 0.35 ml/min wasutilized for the separation of a mixture of alkylphenones andalkylbenzenes. The results of the separation are shown in FIG. 6, whichdepicts a plot of log k' vs. carbon number for each of the alkylphenoneand alkylbenzene solutes present in the mixture. Reduced plate heightswere calculated for each solute, and compared with the reduced plateheights calculated for the same solutes separated on a column packedwith carbon-clad zirconia prepared by deposition of carbon fromn-heptane (see Example 16). This comparison indicated that thechromatographic efficiency of the material prepared with n-butanol isgenerally greater than that of the material prepared with n-heptane.Table 25-1 lists the reduced plate height values:

                  TABLE 25-1                                                      ______________________________________                                        Comparison of CVD n-Butanol and                                               CVD n-Heptane Chromatograghic Efficiency                                                    CVD n-Butanol                                                                             CVD n-Heptane                                       Solute        h.sup.1     h                                                   ______________________________________                                        Butylbenzene  4.1         5.8                                                 Butylphenyl Ether                                                                           7.4         10.3                                                Valrophenone  5.0         5.9                                                 Nitrobenzene  5.2         4.7                                                 ______________________________________                                         .sup.1 h = reduced plate height                                          

EXAMPLE 26 Polybutadiene-Coated Carbon-Clad ZrO₂ Spherules

In order to improve the efficiency and loading of the support materialbut retain the shielding of the carbon-clad surface, carbon-cladinorganic oxide particles were coated with a thin layer of polybutadienepolymer as follows:

An 8 g sample of porous carbon-clad ZrO₂ spherules was preparedaccording to Example 9. Following chemical vapor deposition, theresulting carbon-clad spherules were dried for 8-10 hours in a vacuumoven at 70°-100° C. A surface area measurement of 39.0 m² /g wasobtained. A 1.01% (wt/vol) solution of polybutadiene (PBD) (avg. m.w.4500, obtained from Aldrich Chemical Co., Milwaukee, Wis.) pre-polymerwas then made in hexane. 20 ml of the PBD/hexane solution were added tothe sample of carbon-clad spherules in a 100 ml flask, at 0.7 mgPBD/hexane solution per square meter of total surface area of thecarbon-clad spherules to be coated.

Next, the volume of hexane in the PBD prepolymer solution was adjustedto 5 ml of hexane per gram of packing material by adding hexane. Thesolution was then sonicated for 5 minutes while a vacuum was applied tothe reaction flask, in order to ensure that the pores were completelywetted with prepolymer solution. The reaction flask was then capped andshaken gently for 4 hours to allow the prepolymer to diffuse completelyinto the pores of the carbon-clad material.

At the end of the 4 hours, 2.5 ml of a solution of 53.61 mg dicumylperoxide (DCP), a free radical initiator, obtained from Pfaltz andBauer, Waterbury, Conn., in 25 ml of hexane, were added to the reactionflask. The flask contents were agitated overnight. Following agitation,the flask was placed in a rotary evaporator and the solvent was slowlyevaporated with gentle heating at 35°-40° C. under an intermittentlyapplied vacuum. A round-bottomed flask with a side baffle was used whenremoving the solvent, to facilitate particle bed mixing. In this manner,a thin uniform pre-polymer/initiator film was created on the surface ofthe spherules.

In order to allow the polymer to more completely coat the surface, thespherules were warmed to 100° C. for 30 minutes. The temperature wasthen raised to 145° C. for another 30 minutes to activate thecross-linking initiator. The cross-linking reaction was completed byraising the temperature to 155° C. for an additional 4 hours.

The resulting polymer-coated spherules were allowed to cool for 0.5 hourwhile stored under vacuum. After cooling, the spherules weresequentially rinsed with 100 ml per gram of spherules of each of thefollowing solvents: hexane, dichloromethane, tetrahydrofuran, andfinally hexane again, in order to remove any residual unpolymerizedprepolymer or initiator from the spherules.

EXAMPLE 27 Evaluation of Polymer-Coated, Carbon-Clad ZrO₂ Spherules asHPLC Support

A. Chromatographic Nature

A 4.5 g sample of the carbon-clad, PBD-coated spherules of Example 26were packed in a 12.5×0.46 cm HPLC column using an upward slurry packingtechnique. 5 μl of a mixture of alkylphenones and alkylbenzenes wereinjected onto the packed column. A 50% THF/50% water mobile phase wasused at 35° C. FIG. 7 depicts a plot of log₁₀ (capacity factor, k') vs.carbon number for each alkylphenone and alkylbenzene solute. Thereversed-phase character of the polymer-coated packing material isdemonstrated by the linear relationship between log₁₀ (k') and carbonnumber of the homologous series of alkylbenzenes and alkylphenones.

FIG. 7 also indicates that the alkylbenzenes were retained by thissupport to a greater extent than were the alkylphenones. This elutionorder is typical of conventional silanized bonded reversed phasesupports, and is in contrast to what was observed withnon-polymer-coated, carbon-clad surfaces (see FIG. 3). The order ofretention shown in FIG. 7 indicates that the retention displayed by thissupport material is primarily due to its polymer coating, rather than toits carbon cladding.

B. Column Efficiency

The efficiency of a 12.5×0.46 cm HPLC column packed with thecarbon-clad, PBD-coated ZrO₂ spherules prepared according to Part Aabove, was examined by a flow rate study. FIG. 8A indicates thatpropylbenzene, butylphenyl ether and butyrophenone exhibited minimumreduced plate heights of 3.5, 4.4 and 15.5, respectively, with thevalues for propylbenzene and butylphenyl ether lying quite close to thetheoretically optimum value of 2-3. In contrast, non-polymer-coated butcarbon-clad supports display a significantly reduced efficiency, asindicated by the higher minimum reduced plate heights shown in FIG. 8B.

C. Loading Capacity

A loading study of a 12.5×0.46 cm HPLC column packed with thecarbon-clad, PBD-coated spherules according to Part A above was nextperformed. The solute for this study was butylphenyl ether, and themobile phase was 50% THF/50% water, maintained at 35° C. and a flow rateof 1 ml/min. FIG. 9A depicts a plot of reduced plate height and capacityfactor vs. solute loading, and indicates that the capacity factor andreduced plate height remained relatively constant over the broad rangeof loadings examined. At a very high solute loading, the reduced plateheight increased slightly. These results demonstrate that thepolymer-coated support has a high solute loading capacity. In contrast,non-polymer-coated but carbon-clad supports display a much lower loadingcapacity under similar conditions, as demonstrated by the decrease incapacity factor with the increase in solute concentration as shown inFIG. 9B.

In summary, the results of parts B and C above indicate that the presentpolymer-coated carbon-clad support has a greater efficiency andsample-loading capacity than a non-polymer-coated but carbon-cladsupport.

D. Alkaline Stability

A 12.5×0.46 cm HPLC column prepared according to Part A above was testedfor alkaline stability by flushing the column with a 50%/50% (v/v)methanol/pH 12 aqueous NaOH solution at 80° C., and monitoring theretention of benzene. A plot of capacity factor (k') vs. column volumesof mobile phase passed through the column is depicted in FIG. 10. FIG.10 indicates that retention of solute remained relatively constant overa wide range of volumes of alkaline mobile phase. The scatter of thepoints between 1000 and 1440 column volumes is due to benzene loss fromthe sample vial as the experiment progressed. At 1440 column volumes, anew sample of benzene was placed in the autosampler.

The substantially constant capacity factor and reduced plate height overincreasing column volumes of alkaline mobile phase shown in FIG. 10demonstrate the pH stability of the support. If the support was not pHstable, and had begun to dissolve, a very rapid increase in reducedplate height and a drop in capacity factor would have been observed. Thecarbon analysis results presented in Table 27-1 are a further indicationof the pH stability of the support.

                  TABLE 27-1                                                      ______________________________________                                        Carbon Analysis Results                                                       Source        % C         % H    % N                                          ______________________________________                                        Head of Column                                                                              5.3         0.4    <0.1                                         Middle of Column                                                                            5.2         0.4    <0.1                                         End of Column 5.3         0.4    <0.1                                         New Column    5.3         0.3    <0.1                                         ______________________________________                                    

E. Chromatogram

A mixture of alkylphenones was separated on a 12.5×0.46 cm HPLC columnpacked with carbon-clad, polybutadiene-coated spherules according toPart A above. A 1.0 ml/min. mobile phase of 50% THF/50% water was usedat 35° C. FIG. 11 depicts the chromatogram obtained from thisseparation. The peaks shown in FIG. 11 represent, from left to right,propiophenone, butyrophenone, valerophenone, hexanophenone andheptanophenone, respectively.

F. Physical Structure

FIG. 12 is a schematic depiction of a porous polymer-coated, carbon-cladZrO₂ particle of the present invention.

The invention has been described with reference to various specific andpreferred embodiments and techniques. However, it should be understoodthat many variations and modifications may be made while remainingwithin the spirit and scope of the invention.

What is claimed is:
 1. A particle comprising an inorganic oxide core, acarbon cladding on said core, and a cross-linked polymer coating on saidcarbon cladding, wherein said inorganic oxide core has a diameter ofabout 1μ to about 1 cm.
 2. The particle of claim 1 which is a spherule.3. The spherule of claim 2 wherein the polymer coating comprises ahydrophobic polymer coating.
 4. The spherule of claim 3 wherein thehydrophobic polymer coating comprises polybutadiene.
 5. The spherule ofclaim 2, wherein the polymer coating comprises a hydrophilic polymercoating.
 6. The spherule of claim 5 wherein the hydrophilic polymercoating comprises a hydrophilic polymer selected from the groupconsisting of polyvinylalcohol, poly(ethylene glycol),polyvinylpyrollidone, polyethyleneimine, poly(butadiene maleic acid),polysiloxane, and poly-l-histidine, and dextran.
 7. The particle ofclaim 1 which has a diameter of about 2-1000 microns.
 8. The particle ofclaim 1 which has a surface area of about 2-80 m² /g.
 9. The particle ofclaim 1 which is porous and has a pore size of about 50-1000 Å.
 10. Theparticle of claim 1 wherein said inorganic oxide is selected from agroup consisting of Group II, Group III and Group IV metals.
 11. Theparticle of claim 10 wherein said inorganic oxide is selected from thegroup consisting of HfO₂, ZrO₂, SiO₂, Al₂ O₃, TiO₂, and MgO.
 12. Theparticle of claim 11 wherein said inorganic oxide is ZrO₂.
 13. Theparticle of claim 12 wherein said ZrO₂ core has a surface area of about5-300 m² /g.
 14. The particle of claim 13 wherein said ZrO₂ core has asurface area of about 15-100 m² /g.
 15. The particle of claim 12 whereinsaid ZrO₂ core is porous and has a pore size of about 20-5,000 Å. 16.The particle of claim 15 wherein said ZrO₂ core has a pore size of about60-1,000 Å.
 17. The particle of claim 12 wherein said ZrO₂ core has adiameter of about 1-500μ.
 18. The particle of claim 17 wherein said ZrO₂core has a diameter of about 2-50μ.
 19. The particle of claim 12 whereinsaid carbon-clad ZrO₂ core has a surface area of about 5-300 m² /g. 20.The particle of claim 19 wherein said carbon-clad ZrO₂ core has asurface area of about 15-100 m² /g.
 21. The particle of claim 12 whereinsaid carbon-clad ZrO₂ core is porous and has a pore size of about20-5,000 Å.
 22. The particle of claim 21 wherein said carbon-clad ZrO₂core has a pore size of about 60-1,000 Å.
 23. The particle of claim 12wherein said carbon-clad ZrO₂ core has a diameter of about 1-500μ. 24.The particle of claim 23 wherein said carbon-clad ZrO₂ core has adiameter of about 2-50μ.
 25. The particle of claim 1 wherein said carboncladding has a thickness which does not exceed about 20 Å.
 26. A packingmaterial useful as a stationary phase in a liquid chromatography column,comprising a plurality of the polymer-coated carbon-clad inorganic oxideparticles of claim
 1. 27. A particle comprising an essentiallynon-porous inorganic oxide core, a carbon cladding on said core, and acrosslinked polymer coating on said carbon cladding.
 28. The particle ofclaim 1 which is a spherule.
 29. The particle of claim 1 wherein theinorganic oxide core is ZrO₂.
 30. A particle according to claim 1wherein said inorganic oxide core has a diameter of about 0.4-7μ. 31.The particle of claim 1 wherein said inorganic oxide core has a surfacearea of about 0.1-3 m² /g.